Question

A water tank can be filled by an inlet pipe in 10 hours. It takes 3 times as long for the outlet pipe to empty the tank. How long will it take to fill the tank if both pipes are open?

Answer 1

let the volume of the tank is V

the inlet pipe fills the tank in 10 hours, amount of volume = V

then 1 hour it fills = V/10

similarly for outlet pipe

the outlet pipe empties the tank in 30 hours, amount of volume = V

then 1 hour it empties = V/30

Volume of the tank when both the pipes are simultaneously open to fill any point of time t =

V/10*t - V/30*t

now when it will be full, its volume would be V

V/10*t - V/30*t = V

2/30 t = 1

t = 15 hours.

so answer is 15 hours.