Question 158

Pipe A can fill a tank in 8 hours while another pipe B can fill it in 16 hours. A third pipe C can empity the full tank in 32 hours. All three pipes are opened simutaneously. In what time will an empity tank be filled ?

Solution

Pipe A 1 hour work = 1/8

Pipe B 1 hour work = 1/16

Pipe C 1 hour work = - 1/32

Here negative sign shows that it is doing negative work

Now when all pipes are opened simultaneously then 1 hour combined work = 1/8 + 1/16 - 1/32

= 5/32

So time taken by all pipes to fill the tank = 32/5 hours = 6.4 hours

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