Question

A pipe fills a barrel with vinegar in 20 minutes. A release valve on the barrel, used for drainage, can empty the barrel in 40 minutes. A new employee mistakenly left the drainage valve open as he turned on the pipe to fill a barrel. How long will it take to fill the barrel if the pipe is filling at the same time the valve is emptying?

Answer 1

40 minutes

Explanation:

We have a load and a discharge, given by a speed that would be a barrel / minute.

Which means that the loading rate is: 1/20

And the discharge rate: 1/40

Since they are contrary, the result would be the subtraction between these two rates:

1/20 - 1/40 = 1 / x

1 / x = 0.025

x = 1 / 0.025

x = 40

Which means it will take 40 minutes to fill under the mentioned conditions