The two pumps working together would pump out water at a rate of 100 gallons per minute. To determine the time it takes to completely pump out the water from the basement, we need to determine the volume of the water in the basement. The dimensions of the basement is 40 feet by 50 feet (given elsewhere) while the depth of the water is said to be 16 inches. From these dimensions, we can calculate for the volume as follows:
V = length x width x depth
length = 50 feet
width = 40 feet
depth = 16 inches ( 1 foot / 12 inches ) = 1.33 feet
V = 50 x 40 x 1.33 = 2666.67 ft^3 = 19948.05 gal
Time = V / rate
Time = 19948.05 gal / 100 gal / min
Time = 199.48 min
