Question

Two pipes A and B can fill a tank in 60
hours and 40 hours respectively and pipe
C can empty the tank in 15 hours. If pipes
A and B are opened for 12 hours, then
pipe C is also opened. After how many
hours, the tank will be emptied?
A. 15 hours
B. 20 hours
C. 12.5 hours
D. 10 hours
E. None of these
​

Answer 1

Answer:

Answer

Step-by-step explanation:

As given in the Q ,

Pipe A can fill the tank in 15 hours

So , in 1 hour A pipe can fill 1/15 th part of the tank .

Pipe B can fill the tank in 20 hours

So ,in 1 hour B pipe can fill 1/20 th pat of the tank .

In 1 hour A&B together can fill 1/15 +1/20 = 7/60 part of the tank . Now , C can empty the tank in 25 hours .

In 1 hour C pipe can empty 1/25 th part of the tank .

If all the three pipes are kept open ,in 1 hour ,60/7 — 1/25 = 23/300 part of the tank get filled. Acc. to the question ,all the three pipes kept open for 10 hours .

So ,in 10 hours 23/300 ×10 =23/30 part of the tank get filled . Now pipe c is closed after 10 hours .

So the reaining 1–23/30 = 7/30 part of the tank can be filled by A&B pipe in 7/30 ÷7/60 = 7/30 ×60/7 = 2 hours

Ans: 2 hours .