Bihar Police Constable Model Paper 7

Given:
A tank can be filled by tap A in 5 hours, by B in 4 hours, C can empty it in 8 hours
Calculation:
Efficiency of A = 1/5, of B = 1/4, C = -1/8
Time Taken by A, B, C ∝ 1/Efficiency = (1/5 + 1/4 – 1/8) = (8 + 10 – 5)/40 = 13/40
∴ Time Taken by A, B, C = 40/13 hours