Re: Working together, 7 identical pumps can empty a pool in 6 hours. How many hours will it take 4 pumps to empty the sa

Let the total amount of work required =42 units
In 6 hours work done =42 hours => so each hour work done =42/6 =7 unit /hr
since 7 pumps are working so total 1unit work per hour is done by each pump.
Hence 4 pumps will do 4 unit of work per hour
Total time required =42/4=21/2=10 1/2
Hence E.