Question

Two pipes can fill a tank in 10 hours and 12 hours respectively while a third pipe empties the full tank in 20 hours.

If all the three pipes operate simultaneously, in how much time will the tank be filled?

(1) 6 hrs 45 min
(2) 7 hrs 30 min
(3) 7 hrs 15 min
(4) 7 hrs 45 min

Answer 1

10*12*20/12*20+10*20-10*12
=2400/240+200-120
= 15/2
=7hrs 30mins