college algebra

Question

One pump can empty a pool in 7 days, whereas a second pump can empty the pool in 11 days. How long will it take the two pumps, working together, to empty the pool? 

It will take the two pumps ? days to empty the pool together.

If needed, round answer to 3 decimal places.

Answer 1

the work rates are 1/7 pool per hour and 1/11 pool per hour

their combined work rate is:

1/7 + 1/11 = (11+7)/77 = 18/77

working together they will empty the pool in:

77/18 = 4.27 hours

4 hours 16 minutes 40 seconds