Question

Two pipes a and b can fill a tank in 6 hours and 4 hours respectively. If they are opened on alternate hours and if pipe a is opened first, in how many hours the tank shall be full

Answer 1

Explanation:

A's work in 1 hour 1/6

, B's work in 1 hour = 1/4

(A + B)'s 2 hour's work when opened alternately = (1/6+1/4)=5/12

(A + B)'s 4 hour's work when opened alternately = 10/12 =5/6

Remaining part = (1-5/6) =1/6

Now,  it is A's turn and 1/6

part is filled by A in 1 hour.

Total time taken to fill the tank = (4 + 1) hrs = 5 hrs.