Pipes A, B, and C can fill a tank in 15, 30 and 40 hours, respectively. Pipes A, B, and C are opened at 6 a.m. and 10 a.m., respectively, on the same day. When will the tank be full?
Show answer & explanation
Correct answer: A
Explanation
The correct answer is Option 1 i.e. 3 : 20 p.m.
Pipes A, B, and C can fill a tank in 15, 30 and 40 hours
LCM(15, 30, 40) = 120 = Total work
Efficiency of A = 120/15 = 8 units
Efficiency of B = 120/30 = 4 units
Efficiency of C = 120/40 = 3 units
So
From 6 am - 8 am, only A works
Work completed = 2 × 8 = 16 units
From 8 am - 10 am, A and B work
Work completed = 2 × 12 = 24 units
Work remaining = 120 - 16 - 24 = 80 units completed by A, B, and C together.
Time required = 80/(8 + 4 + 3) = 5(1/3) hours = 5 hours 20 minutes
So, Tank fills = 10 am + 5 hours 20 minutes = 3 pm 20 minutes