A tank holds 1,200 litres of water. Water is drawn out at 45 litres per hour while a pipe refills it at 20 litres per hour. After how many hours will 900 litres be left?

Question

Accepted Answer

12. The tank loses 45 − 20 = 25 litres each hour, so 1200 − 25t = 900 → 25t = 300 → t = 12 hours. Check: 12 × 25 = 300 litres lost, leaving exactly 900. The trap 6.67 uses only the 45 litres drawn out and ignores the refill; 48 is how long the tank would take to empty completely.

A tank holds 1,200 litres of water. Water is drawn out at 45 litres per hour while a pipe refills it at 20 litres per hour. After how many hours will 900 litres be left?

Step-by-Step Solution

Key idea: Variable on both sides

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