AlgebraEasy–MediumEvaluating a linear drain model
Algebra practice question
A swimming pool holds 40,000 litres and is drained at a constant rate. After 3 hours, 31,000 litres remain. How many litres remain after 8 hours?
Answer: 16000
The pool loses 9,000 litres in 3 hours, so 3,000 per hour: 40,000 − 3,000(8) = 16,000.
Common wrong answers
- If you answered 24000
- 24,000 is the amount drained in 8 hours, not the amount remaining.
- If you answered 25000
- 25,000 comes from subtracting 3,000 × 5 from 40,000, counting only the hours after the third.
- If you answered 31000
- 31,000 is the amount after 3 hours.
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