math
posted by robin on .
3 pumps, working 6 hours a day, can empy a water tank in 2 days. How many hours a day must 9 pumps work to empty the same tank in 1 day?

3 pumps > working 6 hours  2 days
6 pumps > working 6 hours  1 day
1 pump > working 36 hrs  1 day
9 pumps > working 4 hrs  1 day
or
it takes 18 pumphrs running for 2 days
it takes 36 pumphrs to do it in 1 day
so 9 pumps would take 4 hrs to do it in 1 day