Pipes A, B and C can fill a tank is 15, 30 and 40 hours, respectively. Pipes A, B and C are opened at 6 a.m., 8 a.m. and 10 a.m., respectively, on the same day. When will the tank be full?

Answer: Option A

A → 6 am → 10 am = 4 × 8 = 32
B → 8 am → 10 am = 2 × 4 = 8
120 - 40 = 80
A + B + C = $$\frac{80}{15}$$ = 5 hr 20 min
10 am + 5 hr 20 min
3 : 20 pm