A 9,000-litre tank is filled by pumps P and Q delivering 150 and 100 litres per minute. P is switched on first; Q is switched on when the tank is one-third full; and P breaks down when the tank is two-thirds full. How long does the whole filling take?

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Accepted Answer

62 min. Each third is 3,000 L. P alone: 3000/150=20 min; both: 3000/250=12 min; Q alone: 3000/100=30 min. Total 62 min. (36 min assumes both pumps run throughout.)

A 9,000-litre tank is filled by pumps P and Q delivering 150 and 100 litres per minute. P is switched on first; Q is switched on when the tank is one-third full; and P breaks down when the tank is two-thirds full. How long does the whole filling take?

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