One pump can empty a pool in 3 days, whereas a second pump can empty the pool in 14 days. How long will it take the two pumps, working together, to empty the pool?
Rate of first pump = 1/3
rate of 2nd pump = 1/14
combined rate = 1/3 + 1/14 = 17/42
Time to do the job at combined rate = 1/(17/42) = 42/17 days
= appr 2.5 days