Question

It can take 12 hours to fill a swimming pool using two pipes. If the pipe of
larger diameter is used for four hours and the pipe of smaller diameter for
9 hours, only half of the pool can be filled. How long would it take for each
pipe to fill the pool separately ?
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Answer 1

larger pipe - 8 hours

Smaller pipe - 18 hours

Answer 2

let the pipe of larger diameter =A

work done in filling half tank =

1/4+1/9

=9+4/36

13/36=half filling of water

full filling =13/72

first pipe time =13/72*4

second pipe time =13/72*9

I hope now you can solve it