Correct option is D
Given:
Pipe A fills the cistern in 52 minutes
Pipe B fills the cistern in 65 minutes
Both pipes are opened together
The cistern is completely filled in 60 minutes
Concept Used:
If a pipe fills 1 tank in t minutes, its rate is per minute.
Total work = 1 (full tank)
Solution:
Pipe A is turned off after x minutes
Work by A in x minutes =
Work by B in 60 minutes =
x = min