Pipes A and B can fill a tank in 12 minutes and 15 minutes, respectively. The tank when full can be emptied by pipe C in x minutes. When all the three pipes are opened simultaneously, the tank is full in 10 minutes. The value of x is:
Show answer & explanation
Correct answer: C
Explanation
The correct answer is option 3 i.e. 20.
Let the total work = LCM of 12 and 15.
Total work = 60 units.
Efficiency of A = 60/12 = 5 units/minutes.
Efficiency of B = 60/15 = 4 units/minutes.
If A, B and C work together then can fill the tank in 10 minutes.
Combined efficiency of them = 60/10 = 6 units/minutes
5 + 4 + C = 6
C = -3.
Time taken by C to empty the tank = 60/3 = 20 minutes.
x = 20 minutes.