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## Homework Statement

The problem is as follows

" 2 pipes fill cistern with water in 4 and 6 hours respectively.If the first pipe in 4 and 6 hours

respectively . if the first pipe be opened first and the pipes be opened alternatively one at a time for 1 hour each, in how many hours will the cistern be filled up"

My attempt:

I first took that in 1 hour first pipe fills 1/4th of tank and second pipe 1/6 thof tank

.: in 2 hours they fill 1/4+1/6= 5/12th of tank

in 1hour they fill 5/24 th of tank

.: they fill the tank in 24/5 hours

But the problem is my book's answer is 19 hours.I don't know how that is possible because if they alone fill it in 4 and 6 hours then if they are working together the time should be less.

Please help me!