14. 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 the tank will be filled?.
A.7hrs B.7 hrs 30 mm.
C.8hrs D.8 hrs. 30 mm.
Answer: 7 hrs 30 mm.
Explanation: Net part filled in 1 hour = (1/10) + (1/12) + (1/20) = 8/60 = 2/15
The tank will be full in 15/2 hrs = 7 hrs 30 min.
