# One pump can fill a tank with oil in 4 hours. A second pump can fill the same tank in 3 hours. If both pumps are used at the same time, how long will they take to fill the tank?

Nov 19, 2016

$1 \frac{5}{7}$hours

#### Explanation:

First pump can fill the tank in 4 hours. So, In 1 hour it ill fill $\frac{1}{4}$th of the tank.

Same way second pump will fill in 1 hour = $\frac{1}{3}$rd of the tank.

If both pumps are used at the same time, then in 1 hour they will fill

$\text{ } \frac{1}{4} + \frac{1}{3} = \frac{3 + 4}{12} = \frac{7}{12}$th of the tank.

Therefore tank will be full = $1 \div \frac{7}{12} = \frac{12}{7} = 1 \frac{5}{7} \text{ }$hours