Rate problems often fail before any difficult arithmetic begins. A learner reads “$12 per 3 notebooks”, “60 km per hour” or “4 litres per minute” and remembers only the numbers. The word per quietly disappears, so the quantity loses its denominator. Twelve dollars becomes a price with no item count attached. Sixty kilometres becomes a distance rather than a speed. Four litres becomes an amount rather than a flow rate.
This volume develops one examination habit: keep every “per” attached to the quantity it is dividing by. A rate is a comparison of unlike quantities. The denominator tells you the unit basis: per item, per minute, per litre, per person, per kilometre. Before multiplying or dividing, write the full unit meaning. That unit often tells you which operation is sensible.
The goal is not to teach advanced dimensional analysis. It is to make Primary 6 rate reasoning visible. When the unit rate is correct, scaling becomes straightforward. When the “per” quantity is lost or reversed, the arithmetic can remain neat while the answer describes the wrong thing.
A rate contains two quantities
Speed compares distance with time; unit price compares money with items; flow rate compares volume with time.
Keep both units visible until the target is clear.
Per means divided by a basis quantity
$3 per notebook means $3 for one notebook.
The denominator basis can be one unit or several units, depending on the given rate.
A unit rate uses one denominator unit
If 5 notebooks cost $20, the unit rate is $4 per notebook.
Finding one unit can simplify comparison and scaling.
Not every problem requires a unit rate
You can scale 5 notebooks for $20 directly to 15 notebooks for $60 without explicitly finding $4 per notebook.
The representation is flexible as long as the ratio stays attached to the right quantities.
Reverse rates are different quantities
60 km per hour is not the same as 1 hour per 60 km.
Both can describe the same constant motion, but they answer different questions and carry different units.
Unit conversion must happen on the correct side
If speed is in km/h and time is in minutes, convert either the time or the speed basis before combining them.
Do not change distance units accidentally while trying to change time units.
The denominator controls multiplication and division
If the rate is $4 per notebook and you want 7 notebooks, multiply by 7 notebooks.
The notebook units conceptually cancel, leaving dollars.
To find quantity from total and rate, divide
If $28 is spent at $4 per notebook, 28 ÷ 4 gives 7 notebooks.
The answer unit comes from removing dollars against dollars per notebook.
To find rate from total and quantity, divide total by basis quantity
$28 for 7 notebooks gives $4 per notebook.
Reversing the division gives notebooks per dollar, a different rate.
Average rate needs total-over-total structure
Average speed over a whole journey depends on total distance divided by total time.
Do not average two speeds directly unless the conditions make that appropriate.
Per-person quantities depend on group size
If 24 bottles are shared among 6 pupils, the unit amount is 4 bottles per pupil.
A change in pupil count changes the per-person rate even if total bottles stay fixed.
Per-pack rates can hide a second step
$18 for a pack of 6 means $3 per item.
If the question asks for 4 packs, you may scale the pack rate rather than item rate.
Compound rates need both units
Kilometres per hour, litres per minute and dollars per kilogram each have a numerator and denominator.
Dropping either unit makes the rate incomplete.
A rate can be constant or variable
A constant-rate problem allows direct proportional scaling.
If the rate changes during the journey or process, split the problem into stages.
Context decides whether fractional answers make sense
A rate can be fractional even when the underlying items are whole.
$2.50 per ticket is meaningful; 2.5 tickets as a final count may not be.
A six-step rate-control routine
- Write the rate with both units.
- Identify the numerator quantity and denominator basis.
- Match the target to the rate: total, quantity or unit rate.
- Convert units if numerator or denominator units are incompatible.
- Choose multiplication or division from the unit meaning.
- Check the final unit and whether the context allows the numerical form.
Thirty-one worked “per” cases
Notebook price
5 notebooks cost $20.
The likely rate error is 20 treated as per-notebook price. 20 ÷ 5 = $4 per notebook.
The denominator is notebooks, so the unit rate is dollars per notebook. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Buying 12 notebooks
Notebooks cost $4 each.
The likely rate error is dividing instead of multiplying. 12 × $4 per notebook = $48.
The notebook count scales the rate up to a total cost. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Finding notebook count
$36 is spent at $4 per notebook.
The likely rate error is multiplying total by rate. 36 ÷ 4 = 9 notebooks.
Total dollars divided by dollars per notebook leaves notebooks. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
60 km per hour
A car travels at 60 km/h for 3 hours.
The likely rate error is rate used as distance only. 60 × 3 = 180 km.
Hours cancel the per-hour basis conceptually. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
90 km in 1.5 hours
A car travels 90 km in 1.5 h.
The likely rate error is reversing division. 90 ÷ 1.5 = 60 km/h.
Distance divided by time gives speed. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Minutes versus hours
A cyclist travels at 12 km/h for 30 minutes.
The likely rate error is 30 treated as 30 hours. 30 minutes = 0.5 hour; distance = 12 × 0.5 = 6 km.
Time units must match the denominator of the rate. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Flow rate
A tap fills at 3 L/min for 8 minutes.
The likely rate error is rate treated as final volume. 3 × 8 = 24 L.
Minutes scale litres-per-minute into litres. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Find filling time
A container needs 30 L at 5 L/min.
The likely rate error is multiplying volume by rate. 30 ÷ 5 = 6 minutes.
Litres divided by litres per minute leaves minutes. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Unit price by kilogram
2 kg of fruit cost $9.
The likely rate error is 9 ÷ 2 ignored. Unit price is $4.50 per kg.
The rate can be decimal even when the number of kilograms was whole. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Cost for 5 kg
Fruit costs $4.50/kg.
The likely rate error is dividing 5 by 4.5. 5 × 4.50 = $22.50.
Kilograms scale the dollars-per-kilogram rate. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
People per table
32 pupils sit at 4 pupils per table.
The likely rate error is rate inverted. 32 ÷ 4 = 8 tables.
Pupils divided by pupils per table gives tables. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Seats per bus
Each bus seats 40 pupils; 81 pupils travel.
The likely rate error is raw quotient reported. 81 ÷ 40 = 2.025 buses, but 3 whole buses are required.
The rate solves capacity, then context constrains the final count. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Pages per day
A reader completes 18 pages per day for 5 days.
The likely rate error is pages and days swapped. 18 × 5 = 90 pages.
The denominator is days. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Days to finish
A 144-page book is read at 18 pages per day.
The likely rate error is multiplication chosen. 144 ÷ 18 = 8 days.
Total pages divided by pages per day gives days. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Cost per 3 items
Three pens cost $7.50.
The likely rate error is treating 7.50 as per one. Unit price is $2.50 per pen.
The original basis is three pens, not one. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Scaling per 3 items
Three pens cost $7.50; buy 12 pens.
The likely rate error is unit rate not required but ratio lost. 12 is four groups of three, so total cost is 4 × 7.50 = $30.
The per-3 rate can scale directly when the group count is clear. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Water per person
18 L is shared equally among 6 people.
The likely rate error is person denominator lost. 3 L per person.
The total volume remains 18 L; the rate describes allocation. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Changing group size
The same 18 L is shared among 9 people.
The likely rate error is old rate reused. 18 ÷ 9 = 2 L per person.
The denominator changed, so the unit rate changes. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Journey with two speeds
A car travels 1 h at 60 km/h, then 2 h at 30 km/h.
The likely rate error is averaging speeds as 45 km/h. Total distance = 60+60=120 km; total time=3 h; average speed=40 km/h.
Average speed is total distance per total time. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Equal-time speeds
A car travels 1 h at 60 and 1 h at 30.
The likely rate error is wrong average claim rejected unnecessarily. Total distance 90 km over 2 h gives 45 km/h.
Here the simple average happens to match because the times are equal. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Equal-distance speeds
A car travels equal distances at 60 and 30 km/h.
The likely rate error is simple average used. Travel times differ, so average speed is not simply 45 km/h.
The rate denominator controls weighting. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Production rate
A machine produces 24 items in 6 minutes.
The likely rate error is 24 items per minute written. Unit rate is 4 items/min.
Divide by the six-minute basis. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Time per item
The same production is expressed as minutes per item.
The likely rate error is same rate assumed. 6/24 = 0.25 min per item.
This reciprocal rate is different but related. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Fuel-like efficiency
A vehicle travels 120 km using 8 L.
The likely rate error is litres per km confused with km per litre. 120 ÷ 8 = 15 km/L.
If the question asks L/km, reverse the division deliberately. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Price comparison
Brand A: $12 for 3 units; Brand B: $15 for 5 units.
The likely rate error is totals compared directly. A is $4/unit; B is $3/unit.
Common unit basis makes the comparison fair. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Recipe scaling
2 cups serve 5 people.
The likely rate error is 2 cups per person assumed. Unit rate is 0.4 cup/person.
Or scale directly to another multiple while preserving the pair. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Serving 15 people
2 cups serve 5 people.
The likely rate error is using 15/2. 15 people is 3 groups of 5, so 6 cups.
The group basis can be scaled without finding per-one first. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Tickets per booklet
A booklet contains 8 tickets; 6 booklets are bought.
The likely rate error is ticket and booklet roles reversed. 8 tickets/booklet × 6 booklets = 48 tickets.
Booklets cancel as the denominator basis. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Fixed fee problem
A service costs $5 plus $2 per item.
The likely rate error is treating total as pure rate. The $2/item part scales, but the $5 fixed fee is added once.
Not every cost relationship is entirely proportional. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Discounted unit price
A pack of 4 costs $12 after a promotion.
The likely rate error is dividing by old price. Current unit price is based on current total: $3/item.
Use the total given for the state being asked about. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
Final unit check
A learner finds 7 after dividing $28 by $4/item.
The likely rate error is answer left unitless. The final answer is 7 items.
The unit confirms what quantity the division produced. Read the units aloud: dollars per notebook, kilometres per hour, litres per minute. If the sentence sounds wrong, the division direction may be wrong.
Now write the target unit before calculating. If the target is hours, arrange the quantities so the distance unit cancels and time remains. This is a simple meaning check, not advanced algebra.
For delayed transfer, change the story noun while preserving the same rate structure. The learner should still identify numerator, denominator and target without relying on familiar wording.
A rate-table clinic
Suppose a table lists 2 kg of rice for $5.60, 5 kg for $14.00 and 8 kg for $22.40. The unit price is $2.80 per kg in every row. This supports a constant proportional price relationship. A learner can compare rows by finding unit price or by checking that both quantity and cost scale together.
Now change the final row to 8 kg for $20.00. The first two rows still show $2.80/kg, but the third does not. The relationship may include a bulk discount. Do not force one constant rate across all rows because two earlier rows matched.
The table therefore teaches two checks: keep each rate attached to its basis, and verify whether the rate is actually constant before scaling beyond the observed pair.
A journey clinic: rate versus amount
A car travels at 50 km/h. After two hours, the distance is 100 km. Fifty is the rate; one hundred is the accumulated distance. If the learner writes “the car’s distance is 50 km/h”, the unit itself reveals that rate and amount have been confused.
If the car then changes to 30 km/h for one hour, the second stage adds 30 km. The total distance is 130 km over three hours. The whole-journey average speed is 130/3 km/h, not either stage speed. Stage rates, stage amounts and whole-journey rate are different quantities.
Use labels such as Stage 1 distance, Stage 2 distance and total time. Long rate problems become easier when each “per” stays attached to its own stage.
A seven-day rate-control cycle
- Day 1: unit price and per-item rates.
- Day 2: speed as distance per time.
- Day 3: flow rates and production rates.
- Day 4: reverse questions finding time, quantity or number of groups.
- Day 5: unit conversions inside rate problems.
- Day 6: variable-rate and fixed-fee cases where proportionality breaks.
- Day 7: delayed mixed practice with final-unit checks.
Parents and tutors: ask what the number is per
When a learner writes a rate number without units, ask “per what?” If the learner cannot answer, the rate has lost its basis. Restore the units before discussing the operation.
When division direction is confused, ask for both possible interpretations: dollars per item and items per dollar, kilometres per hour and hours per kilometre. The learner can then choose the rate the question actually needs.
Do not force every problem through unit-rate form. Direct scaling is efficient when the ratio is clear. The real standard is preserved meaning, not one compulsory method.
Frequently asked questions
Does per always mean divide?
A rate is a quotient relationship, but you may use direct scaling without explicitly performing a per-one division every time.
How do I know which way to divide?
Name the desired rate in words. Dollars per item means dollars divided by items; items per dollar reverses that.
Why do units matter so much?
They identify the numerator, denominator and final quantity, often revealing a reversed operation.
Can a rate be a decimal?
Yes. Rates such as $2.50 per item or 0.4 cup per person are meaningful.
Is average speed the average of two speeds?
Not generally. Use total distance divided by total time unless conditions justify a simpler shortcut.
What if a fixed fee is included?
The relationship is not purely proportional. Scale the per-unit part and add the fixed fee separately.
Official 2026 PSLE Mathematics frame
The 2026 PSLE Mathematics syllabus assesses computation, application in varied contexts and mathematical reasoning. Rate problems require learners to interpret relationships, units and context rather than manipulate numbers alone. See the 2026 PSLE Mathematics syllabus.
Next route
Use the Primary 6 Mathematics Learning Hub for the wider subject route. Return to Vol 0016 for unit-based checking and Vol 0062 for proportional scaling.
The performance rule
Every rate has a denominator. Keep the “per” quantity attached until the final unit tells you that you found the right kind of answer.
