AlgebraVery hardTime to fill a leaking tank
Algebra practice question
A tank is filled by a pipe at 8 litres per minute while a leak drains it at 3 litres per minute. Starting from empty, after how many minutes will the tank hold 120 litres?
Answer: 24
The net rate is 8 − 3 = 5 litres per minute, so 120/5 = 24 minutes.
Common wrong answers
- If you answered 11
- 11 divides 120 by 11, the sum of the rates.
- If you answered 15
- 15 ignores the leak.
- If you answered 40
- 40 uses the leak's rate alone.
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