Question

working together, two pumps can drain a certain pool in 4 hours. if it takes the older pump 9 hours to drain the pool by itself, how long will it take the newer pump to drain the pool on its own?

Answer 1

Answer: Number of hours newer pump needed to drain is given by

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

Step-by-step explanation:

Since we have given that

Number of hours taken by two pumps = 4 hours

Work done by two pumps = $\dfrac{1}{4}$

Number of hours taken by older pump = 9 hours

Work done by older pump = $\dfrac{1}{9}$

According to question, work done by new pump would be

$\dfrac{1}{4}-\dfrac{1}{9}\\\\=\dfrac{9-4}{36}\\\\=\dfrac{5}{36}$

So, Number of hours newer pump needed to drain is given by

$\dfrac{36}{5}=7\dfrac{1}{5}\ hours$