Question

it takes 3 hours for ten pumps to pump 40000l of water ino a dam. how long will it take nine pumps to pump 60000l of water into a dam

Answer 1

40000 L takes 30 pump-hr

so 60000 L takes 45 pump-hr
... one and a half times as much

45 pump-hr / 9 pump = ?

Answer 2

9/10 the pumps, 10/9 the time.
3/2 the volume, 3/2 the time.

10/9 * 3/2 = 5/3 the time.

5/3 * 3 = 5 hours