Pipe A can fill a tank in 22 hours, and pipe B can fill 50% of the tank in 14 hours. Pipe C can empty the tank in 14 hours. If all the pipes are opened at 5:00 am, and pipe C is closed after 3 hours, then at what time (approx) the tank will be filled?

Given:

Pipe A can fill a tank in 22 hours.

Pipe B can fill 50% of the tank in 14 hours.

Pipe C can empty the tank in 14 hours.

Formula Used:

Efficiency = Total work/Time taken

Calculation:

Pipe B can fill full tank = 14 × 2 = 28 hours

Let's assume total work = 308 units (LCM of 22, 28, and 14)

Efficiency of A = 308/22 =14

Efficiency of B = 308/28 =11

Efficiency of C = 308/14 = -22 

Now 

⇒ Work done by all 3 pipes in 3 hours = {14 + 11 + ( -22)} × 3

⇒ 9 unit

Remaining work = 308 - 9 = 299 units

Time required to fill the remaining tank = 299/ (14+11)

⇒ 11.96 ≈ 12 hours

So,

⇒  5:00 AM + 3 hours + 12 hours

⇒ 8:00 PM