Question

An aquarium tank can hold 7200 liters of water. there are two pipes that can be used to fill the tank. the first pipe alone can fill the tank in 48 minutes. the second pipe can fill the tank in 96 minutes by itself. when both pipes are working together, how long does it take them to fill the tank?

Answer 1

The first pipe pumps out

$\dfrac{7200\text{ L}}{48\text{ min}}=\dfrac{150\text{ L}}{1\text{ min}}$

while the second pipe pumps out

$\dfrac{7200\text{ L}}{96\text{ min}}=\dfrac{75\text{ L}}{1\text{ min}}$

So together, both pipes pump out

$\dfrac{150+75\text{ L}}{1\text{ min}}=\dfrac{225\text{ L}}{1\text{ min}}=\dfrac{7200\text{ L}}{32\text{ min}}$

That is, with both pipes filling the tank, it should take 32 minutes total.