Two pipes A and B can fill a tank in 15 minutes and 20 minutes respectively. Both pipes are opened together, but after 4 minutes, pipe A is turned off. What is the total time required to fill the tank?
A
10m 20s
B
11m 45s
C
12m 30s
D
14m 40s
Correct Option:
D
Explanation
A fills 1/15 of the tank per minute and B fills 1/20. Together their rate is 7/60. In 4 minutes they fill 28/60=7/15, leaving 8/15. B alone needs (8/15)÷(1/20)=32/3=10 2/3 minutes = 10 min 40 sec. Total = 14 min 40 sec.
