If it takes 4 identical pipes 2 hours to fill a pool, how many hours will it take 1 pipe alone to fill the same pool? f)16 hrs g)10hrs h)8 hrs j)4 hrs k) none of these

Suppose one pipe alone can fill it in x hour

one hour work of one pipe = 1/x work

one hour work of 4 pipes together = 4/x work

2 hour work of four pipes = 2*( 4/x) = 8/x work

but all four together in 2 hours did complete work that is 1

so 8/x = 1

hence x= 8

so one pipe alone can fill it in 8 hours

Answer : 8