Pipes A and B together usually fill a tank in 6 hours, A alone taking 10 hours. One day, because of low pressure, A ran at half its usual rate and B at three-quarters of its usual rate. How long did the tank take to fill that day?

Question

Accepted Answer

10 h. B's usual rate =1/6-1/10=1/15. That day: 1/2×1/10+3/4×1/15=1/20+1/20=1/10 → 10 h. (9.6 h applies the average factor 0.625 to both.)

Pipes A and B together usually fill a tank in 6 hours, A alone taking 10 hours. One day, because of low pressure, A ran at half its usual rate and B at three-quarters of its usual rate. How long did the tank take to fill that day?

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