Three pipes A, B and C can fill a tank in 5 hours. After working at it together for 2 hours, C is closed and A and B can fill the remaining part in 6 hours. How many hours will take C alone to fill the tank? Choose the correct choice from the following options
A) 8
B) 10
C) 12
D) 14
E) 16
The rate of A+B+C is 1/5 of the tank per hour.   After 2 hours, the tank is 2/5 full.   The rate of A+B is 3/5 * 1/6 = 1/10 of a tank per hour.   The rate of C is 1/5 - 1/10 = 1/10   C can fill the tank in 10 hours.   The answer is 10.
<result>B</result>
Three pipes A, B and C can fill a tank in 5 hours. After working at it together for 2 hours, C is closed and A and B can fill the remaining part in 6 hours. How many hours will take C alone to fill the tank?