Pipe A, B and C are kept open and together fill a tank in t minutes. Pipe A is kept open throughout, pipe B is kept open for the first 10 minutes and then closed. Two minutes after pipe B is closed, pipe C is opened and is kept open till the tank is full. Each pipe fills an equal share of the tank. Furthermore, it is known that if pipe A and B are kept open continuously, the tank would be filled completely in t minutes. How long will C alone take to fill the tank?
Select the correct option:
A) 18	B) 36	C) 27	D) 24	E) 32
A is kept open for all t minutes and fills one-third the tank. Or, A should be able to fill the entire tank in '3t' minutes.   A and B together can fill the tank completely in t minutes. A alone can fill it in 3t minutes.   A and B together can fill 1t of the tank in a minute. A alone can fill 1/t of the tank in a minute. So, in a minute, B can fill 1/t−1/t=2/t. Or, B takes 3/2 minutes to fill an entire tank.   To fill one-third the tank, B will take t/2 minutes. B is kept open for t - 10 minutes.   t/2 = t - 10, t = 20 minutes.   A takes 60 minutes to fill the entire tank, B takes 30 minutes to fill the entire tank. A is kept open for all 20 minutes. B is kept open for 10 minutes.   C, which is kept open for 8 minutes also fills one-third the tank. Or, c alone can fill the tank in 24 minutes. Choice (24)
<result>D</result>
Pipe A, B and C are kept open and together fill a tank in t minutes. Pipe A is kept open throughout, pipe B is kept open for the first 10 minutes and then closed. Two minutes after pipe B is closed, pipe C is opened and is kept open till the tank is full. Each pipe fills an equal share of the tank. Furthermore, it is known that if pipe A and B are kept open continuously, the tank would be filled completely in t minutes. How long will C alone take to fill the tank?