posted by Jaison on .
One pump can empty a pool in 5 days, whereas a second pump can empty the pool in 7 days. How long will it take the 2 pumps, working together, to empty the pool?
Is the answer 2 11/12 days (3 days)
Add the pumping rates in pools per day to get the combined pumping rate.
Rate = 1/5 + 1/7 = 12/35 pools per day
Time required = (1 pool)/(12/35 pool/day) = 35/12 day = 70 hours
That agrees with your answer. Don't round off 35/12 as 3 days. You will be marked wrong.