PRIMARY 4 MATHEMATICS LEARNING GUIDE · BATCH 6 · GUIDE 21
Money questions are decimal questions with a real unit attached. The digits must stay aligned, but the arithmetic also has to preserve what the amounts mean: price, total cost, amount paid, change, money left, difference, budget or combined spending.
This guide develops addition and subtraction of money in decimal notation, change, budgeting, multi-step word problems, estimation, alternative strategies and checking. It is designed to make the relationship visible before the calculation begins.
Series route: return to the Primary 4 Mathematics Learning Hub. For decimal foundations, revisit Decimal Measurement, Place Value and Rounding Accuracy.
Curriculum boundary: Primary 4 includes adding and subtracting money in decimal notation and solving word problems involving those operations. See the MOE Primary Mathematics Syllabus, updated October 2025. The examples and teaching routines below are independently written by eduKate Publishing.
1. Read the amount before calculating
$4.70 means four dollars and seventy cents. $4.07 means four dollars and seven cents. These two amounts are not interchangeable.
The decimal point separates whole dollars from parts of a dollar. Hundredths correspond naturally to cents because one dollar contains one hundred cents.
Say the amount in words before operating on it.
2. Trailing zeros preserve value
$6.5 and $6.50 have the same numerical value, though money is conventionally written to two decimal places.
Writing $6.50 can make place-value alignment easier when adding or subtracting another amount such as $2.75.
3. Add money by aligning place values
Calculate $8.45 + $3.70.
Align dollars, tenths and hundredths:
$8.45 + $3.70 = $12.15.
The decimal points align because the place values align. This is not merely visual formatting.
4. Subtract money by preserving dollars and cents
Calculate $20.00 − $7.68.
The result is $12.32.
Writing $20.00 makes the regrouping visible and protects the cents place.
5. Find change from amount paid minus cost
An item costs $13.75 and a customer pays $20.00. Change is:
$20.00 − $13.75 = $6.25.
Check by adding the cost and change: $13.75 + $6.25 = $20.00.
6. Count up to check change
For $13.75 to $20.00, count up:
$13.75 → $14.00 is $0.25.
$14.00 → $20.00 is $6.00.
Total change = $6.25.
This provides a second route and can catch a subtraction error.
7. Make a whole dollar first
For $7.85 + $3.60, one strategy is to move $0.15 from $3.60 to $7.85.
$7.85 + $0.15 = $8.00, leaving $3.45.
$8.00 + $3.45 = $11.45.
The total is preserved because the same combined money is simply regrouped.
8. Estimate before exact addition
For $18.95 + $7.80, estimate about $19 + $8 = $27.
The exact answer is $26.75, which is plausible.
An answer of $267.50 would fail the scale check immediately.
9. Estimate before finding change
An item costs $27.40 and the customer pays $50. The change should be a little more than $22.
Exact change: $50.00 − $27.40 = $22.60.
Estimation helps detect misplaced decimals before the final answer is accepted.
10. Total cost from several items
A notebook costs $3.85 and a pen costs $1.90. The total is:
$3.85 + $1.90 = $5.75.
If $10 is paid, change is $10.00 − $5.75 = $4.25.
This is a two-step problem: total cost first, then change.
11. Money left after spending
A child has $24.50 and spends $8.75. Money left is:
$24.50 − $8.75 = $15.75.
The answer is smaller than the starting amount because money left the collection.
12. Several spending events need intermediate states
A child starts with $30.00, spends $6.80 and later spends $4.25.
After the first purchase: $23.20.
After the second: $23.20 − $4.25 = $18.95.
Keep the intermediate amount visible so that the second subtraction acts on the correct state.
13. Money can also increase
A child has $12.40 and receives $5.60. The new amount is $18.00.
If $3.75 is then spent, the final amount is $14.25.
The operation sequence follows the event sequence.
14. Budget means compare total cost with available money
A student has a $25 budget. Two items cost $9.80 and $12.45.
Total cost = $22.25.
Money remaining = $25.00 − $22.25 = $2.75.
Because the total cost does not exceed $25, the purchase fits the stated budget.
15. Exceeding a budget requires a difference calculation
A budget is $40.00 and planned purchases total $43.65.
The amount over budget is $43.65 − $40.00 = $3.65.
Do not report $43.65 as the amount over budget. That is the total cost, not the excess.
16. Unknown starting money
After spending $7.25, a child has $18.40 left. How much was there at first?
Restore the spent amount: $18.40 + $7.25 = $25.65.
Check forwards: $25.65 − $7.25 = $18.40.
17. Unknown price from total and known item
Two items cost $14.90 altogether. One costs $6.35. The other costs:
$14.90 − $6.35 = $8.55.
The total is a whole made from two separate item prices.
18. Compare two prices
One item costs $18.60 and another costs $14.85.
The difference is $18.60 − $14.85 = $3.75.
A comparison question asks for the gap, not the total.
19. Common money errors
| Error | Weak link | Repair question |
|---|---|---|
| $4.7 treated as $4.07 | Decimal place value | How many cents does the amount represent? |
| Decimal points not aligned | Place-value addition/subtraction | Are dollars under dollars and cents under cents? |
| Total cost reported as change | Target misunderstood | What amount was paid and what amount must be returned? |
| Budget amount subtracted from one item only | Combined cost not found first | What is the full planned cost? |
| Money left larger after spending | Direction check missing | Did money enter or leave the collection? |
20. Practice laboratory
- Calculate $7.45 + $2.80.
- Calculate $15.00 − $6.38.
- An item costs $12.65 and $20 is paid. Find the change.
- Add $8.75 and $4.60.
- A child has $25.40 and spends $9.85. Find the remainder.
- Two items cost $6.90 and $11.35. Find the total.
- $30 is paid for the items in Question 6. Find the change.
- A budget is $50 and planned purchases total $46.80. Find the amount remaining.
- A budget is $35 and planned purchases total $38.25. Find the amount over budget.
- After spending $4.75, a child has $16.20 left. Find the starting amount.
- Two items cost $19.40 altogether. One costs $8.65. Find the other.
- Find the difference between $21.30 and $16.85.
- Estimate $18.95 + $7.80 before calculating exactly.
- A child has $40, spends $12.75 and then $6.80. Find the final amount.
- A child has $15.50, receives $9.25, then spends $4.60. Find the final amount.
- A $100 budget covers items costing $24.80, $36.45 and $18.75. Find the amount left.
- An item is reduced from $28.90 to $24.50. Find the difference.
- A customer pays $50 and receives $13.65 change. Find the cost.
- A total bill is $27.80. Two known items cost $9.40 and $7.85. Find the cost of the third item.
- Explain one independent check for $20.00 − $13.75 = $6.25.
21. Explained answers
1. $10.25.
2. $8.62.
3. $7.35.
4. $13.35.
5. $15.55.
6. $18.25.
7. $11.75.
8. $3.20.
9. $3.25.
10. $20.95.
11. $10.75.
12. $4.45.
13. Estimate about $27; exact answer $26.75.
14. $20.45.
15. $20.15.
16. Total cost $80.00; amount left $20.00.
17. $4.40.
18. Cost = $50.00 − $13.65 = $36.35.
19. Known items total $17.25; third item = $27.80 − $17.25 = $10.55.
20. Add cost and change: $13.75 + $6.25 = $20.00.
22. Teaching routine: amount, event, target, check
Ask the learner to label every money amount by its role: price, total, amount paid, change, budget, money left or difference. Then choose the operation. After calculation, use estimation or an inverse check.
The reusable route is: read amount → name role → combine or compare → calculate → check → answer in dollars and cents.
23. Where this guide connects next
Money strengthens decimal place value, estimation, before-and-after reasoning and multi-step problem solving. The same discipline of preserving units becomes essential in length, mass and volume.
Continue to Length: Kilometres, Metres, Centimetres and Compound Units →
Editorial control: Wintour House V1.0 · CivDJ · eduKate Publishing.
