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Subtract the starting meter reading
Task reminder
The meter started above zero. How much water did you add?
A tap runs steadily. Its meter reads 20 ℓ at 14:10 and 62 ℓ at 14:17. The meter did not start at zero. Find the tap’s rate during these seven minutes.
Two readings from one meter
At 14:10: 20 ℓ. At 14:17: 62 ℓ.
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Figure data
This table is included in print while it is open.
| Set | Values |
|---|---|
| At 14:10 | 20 ℓ |
| At 14:17 | 62 ℓ |
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Water added: 62 − 20 = 42 ℓ.
Time between the readings: 7 min.
Rate: 42 ÷ 7 = 6 ℓ/min.
Check: seven minutes at 6 ℓ/min adds 42 ℓ, taking the meter from 20 ℓ to 62 ℓ. Dividing 62 by 7 would wrongly include water counted before 14:10.
Task reminder
Which part of the bill do you pay only once?
Take away the one-off fee first
Six identical items and a $3 delivery fee cost $21 altogether. Delivery is charged once. There are no other charges or discounts. Find the price per item before delivery.
One fee and six equal prices
Bill (SGD): 21. Parts: Delivery (SGD): 3; 6 items (SGD): ?. The two parts together make the whole.
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Figure data
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| Quantity | Amount |
|---|---|
| Bill (SGD) | 21 |
| Delivery (SGD) | 3 |
| 6 items (SGD) | ? |
Show workingHide answer
Cost of the items: 21 − 3 = 18 dollars.
Price per item: 18 ÷ 6 = 3 dollars per item.
Check the whole bill: 6 × 3 + 3 = 21 dollars. The delivery fee does not grow with each item, so dividing the whole bill by six does not give the item’s price.
Task reminder
How much do all three hoses supply in the same minute?
Three hoses share one clock
Three identical hoses each supply 5 ℓ/min. All three start together and run steadily for 4 minutes, with no stops or losses. Find their combined output.
Three amounts during the same minute
One shared minute: 5 ℓ; 5 ℓ; 5 ℓ.
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Figure data
This table is included in print while it is open.
| Set | Values |
|---|---|
| One shared minute | 5 ℓ; 5 ℓ; 5 ℓ |
Show workingHide answer
Combined rate: 3 × 5 = 15 ℓ/min.
Combined output: 15 × 4 = 60 ℓ.
Alternatively, each hose supplies 5 × 4 = 20 ℓ; three such amounts total 60 ℓ. The elapsed time is still four minutes. There are three producers, not three successive four-minute waits.
Find a shared running time
Now two identical printers each produce 12 pages per minute. They start together and keep that rate without stopping. How many minutes do they need to produce 120 pages altogether?
Show the time checkHide answer
Together: 12 + 12 = 24 pages per minute.
Time: 120 ÷ 24 = 5 minutes.
Using just one printer’s rate would describe a different arrangement.
Task reminder
Does your time use the same unit as the rate?
Match the time unit before multiplying
A pump supplies 2.4 ℓ/min steadily for three quarters of an hour. Find the total volume shown. The rate uses minutes; the time must use minutes too.
Four equal parts make one hour
One hour: 15 min; 15 min; 15 min; 15 min.
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Figure data
This table is included in print while it is open.
| Set | Values |
|---|---|
| One hour | 15 min; 15 min; 15 min; 15 min |
Show workingHide answer
Time: 3 × 15 = 45 minutes.
Volume: 2.4 × 45 = 108 ℓ.
Check in three fifteen-minute groups: each group supplies 2.4 × 15 = 36 ℓ. Three groups supply 3 × 36 = 108 ℓ. Multiplying by 0.75 without changing the rate would treat 0.75 as minutes.
Task reminder
For how many minutes was the machine actually working?
Count the minutes when the machine works
A printer produces 8 pages per minute while running. It starts at 10:05 and finishes at 10:25, with one five-minute stop inside that interval. It produces no pages during the stop. How many pages does it produce?
| Part of the visit | Time |
|---|---|
| Whole interval | 10:05 to 10:25 |
| Stop inside the interval | 5 minutes |
Show workingHide answer
Elapsed time: 20 minutes.
Printing time: 20 − 5 = 15 minutes.
Output: 8 × 15 = 120 pages.
The five stopped minutes remain part of the visit, but they contribute no output. Using all twenty minutes would predict 160 pages and count the stopped time as working time.
Task reminder
How much water do all the bottles need together?
Fill all the bottles
Eight empty bottles each need 0.5 ℓ. A tap supplies water steadily at 0.8 ℓ/min. Find the total running time needed to supply all the water. Ignore time spent moving bottles; there is no spilling or wasted water.
All eight bottles contribute to the target
First four bottles: 0.5 ℓ; 0.5 ℓ; 0.5 ℓ; 0.5 ℓ. Other four bottles: 0.5 ℓ; 0.5 ℓ; 0.5 ℓ; 0.5 ℓ.
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Figure data
This table is included in print while it is open.
| Set | Values |
|---|---|
| First four bottles | 0.5 ℓ; 0.5 ℓ; 0.5 ℓ; 0.5 ℓ |
| Other four bottles | 0.5 ℓ; 0.5 ℓ; 0.5 ℓ; 0.5 ℓ |
Show workingHide answer
Water needed: 8 × 0.5 = 4 ℓ.
Running time: 4 ÷ 0.8 = 5 minutes.
Check: 0.8 × 5 = 4 ℓ. That equals the combined bottle capacity. Using 0.5 ℓ as the whole target would fill only one bottle.
Before using a rate, identify the amount, the number of units and what each unit means. A meter reading, whole bill or elapsed visit may include a part that does not belong in that relationship.
For a grown-up
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Syllabus and review details
- Primary 5 Mathematics 2025 · 2021-updated-2025-10
- Primary 5 Foundation Mathematics 2025 · 2021-updated-2025-10
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