Pipes A and B can empty a full tank in 15 minutes and 20 minutes, respectively, while pipe C alone can fill the empty tank in 8 minutes. If pipes A, B and C are opened together, then in how many hours will the tank be filled?

Options
a) 2.5
b) 1.5
c) 2
d) 3

Solution

As per question
A can empty a full tank in = 15 minutes
B can empty a full tank in = 20 minutes
C alone can fill the empty tank in = 8 minutes
L.C.M of 15 , 20 , 8
L.C.M = 120 min.
Total work = 120 min.
A efficiency = -8
B efficiency = -6
C efficiency = +15

A, B and C are opened together
A + B + C = – 6 – 8 +15 = 1
Total work = 120
Total time = = 120 min.
60 min. = 1 hour
120 min. = 2 hour

Ans : 2 hrs