Pipe A can fill an empty tank in 18 hours and pipe B in 24 hours. If both the pipes are opened and after 3 hours pipe A is closed, how much time (in hrs) B will take to fill the remaining tank?
Show answer & explanation
Correct answer: A
Explanation
Rate of Pipe A = 1/18 tank/hour
Rate of Pipe B = 1/24 tank/hour
Combined rate of both = 1/18 + 1/24
= (4 + 3)/72
= 7/72 tank/hour
Tank filled in 3 hours = 3 × 7/72
= 7/24
Remaining tank = 1 − 7/24
= 17/24
Only Pipe B will operate.
Time = (17/24) / (1/24) = 17 hours