The given dimensions of the rectangular swimming pool are = 
Length = 20 feet
Width = 12 feet
Height upto which the water should be filled up = 5 feet
So, the total volume of water needed to fill the pool will be = 
 cubic feet
 cubic feet
The water is pumped at a speed of = 30 cubic feet per minute.
So, to fill 1200 cubic feet, the time taken will be = 

Hence, it will take 40 minutes to fill the pool.