A pipe can fill an empty tank in 12 h. After it is kept open for 3 h, another pipe which can fill the tank in 8 h is opened. In how many more hours will the tank be filled?

A pipe can fill an empty tank in 12 h. After it is kept open for 3 h,

1.	A pipe can fill an empty tank in 12 h. After it is kept open for 3 h, another pipe which can fill the tank in 8 h is opened. In how many more hours will the tank be filled?
Answer» `(17)/(7)h` `(18)/(5)h` `(20)/(9)h` `(16)/(5)h` Solution :The part of the tank filled by tap 1 is `(1)/(12)` the part. In 3h, it has filled `3 xx (1)/(12) = (1)/(12)` th part of tank. Remaining part of the tank to be filled = `1-(1)/(4) =(3)(4)`th part of tank. In 1 h, both pipes can fill `((1)/(12) + (1)/(8))` th part of tank. `= (3 + 2)/(24) = (5)/(24)` th part of tank. `(3)/(4)` th of tank can be filled in `((3)/(4))/((5)/(24)) = (18)/(5)` h. Hence, the CORRECT OPTION is (b).