Question

8. A tank is filled in 5 hours by three pipes A, B and C. The pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?

Answer 1

A tank is filled in 5 hours by three pipes A, B and C
so, A+B+C=5 hours

in one hour, A+B+C = 1/5...........(1)

The pipe C is twice as fast as B and B is twice as fast as A
C = 2B
B = 2A.......(2)
C = 2(2A)
C = 4A.........(3)
suppose A alone takes x hours to fill the tank and in one hour, A takes 1/x

then substitute A = 1/x in (2) and (3)
B = 2/x
C = 4/x

A=1/x, B=2/x, C=4/x substitute in (1)
1/x + 2/x + 4/x = 1/5
(1+2+4)/x = 1/5
7*5 = x
x = 35

The pipe A alone takes x = 35 hours to fill the tank

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