AlgebraMediumRate from two readings of a draining pool
Algebra practice question
A swimming pool is being drained at a constant rate. At 1 p.m. it contains 20,000 litres, and at 4 p.m. it contains 14,000 litres. How many litres per hour are being drained?
Answer: 2000
The pool lost 20,000 − 14,000 = 6,000 litres over 4 − 1 = 3 hours: 6,000/3 = 2,000 litres per hour.
Common wrong answers
- If you answered 1500
- 1,500 divides by 4 (the clock reading) instead of by the 3 hours elapsed.
- If you answered 3000
- 3,000 comes from dividing 6,000 by 2, a slip in counting the hours; 1 p.m. to 4 p.m. is 3 hours.
- If you answered 6000
- 6,000 is the total drained over the three hours, not the hourly rate.
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