Pipes A, B and C can fill a tank in 20, 30 and 60 hours, respectively. Pipes A, B and C are opened at 7 a.m., 8 a.m. and 9 a.m., respectively, on the same day. When will the tank be full?

Answer: Option D

Pipe A till 9 O'clock = 3 × 2 = 6
Pipe B till 9 O'clock = 2 × 1 = 2
Remaining work = 60 - 6 - 2 = 52
Time = $$\frac{52}{6}$$
= $$8\frac{4}{6}$$
= 8 hrs 40 min
= 9:00 + 8 hrs 40 min
= 05:40 pm