Question

A tank can be filled by one pipe in four hours and by a second pipe in six hours; and when it is full, the tank can be drained by a third pipe in three hours. If the tank is empty and all three pipes are open, in how many hours will the tank be filled?
8 hours
12 hours
24 hours

Answer 1

quarter plus sixth less third per hour

Answer 2

wait so 12?

Answer 3

first pipe can fill the tank in 4 hours
so in one hour it will fill 1/4 th
second pipe can fill the tank in 6 hours
so in one hour it will fill 1/6 th
third pipe can drain the tank in 3 hours
so in one hour it will drain 1/3rd of the water

so together if we open all the pipies
then we will have
\[\large{{{1}\over{4}} +{{1}\over{6}} −{{1}\over{3}}} \]
is i am correct @estudier

Answer 4

12