Answer: 22.5 hours
Step-by-step explanation:
Let t be the time taken by both of the pumps to drain the pool.
Given: Time taken by pump 1 to drain the pool alone= 9 hours.
Time taken by pump 2 to drain the pool alone= 3 hours.
If both pumps are used simultaneously, then
[tex]\dfrac1t=\dfrac19+\dfrac13\\\\\Rightarrow\ \dfrac1t=\dfrac{1+3}{9}\\\\\Rightarrow\ \dfrac1t=\dfrac49\\\\\Rightarrow\ t=\dfrac94\\\\\Rightarrow\ t=2.25[/tex]
Hence, it will take 22.5 hours to drain the pool if both pumps are used simultaneously.
