Answer:
If the pool is 2/3 filled and then the inlet pipe and drain pipe are opened, it will take 140 hours to fill the pool
Step-by-step explanation:
An inlet pipe can fill the pool in hours = 20
Inlet pipe 1 hour work =
A drain pipe can empty the pool in 21 hours
Drain pipe 1 hour work =
Inlet pipe and drain pipe 1 hour together work =
Now we are given that the pool is 2/3 filled
So, remaining portion to be filled =
So, Inlet pipe and drain pipe fill in hours = 1
So, they can fill 1/3 in hours =
Hence If the pool is 2/3 filled and then the inlet pipe and drain pipe are opened, it will take 140 hours to fill the pool