1.  Three pipes A, B and C can fill a tank in 6 hours. After working at it together for 2 hours, C is closed and A and B can fill the remaining part in 7 hours. The number of hours taken by C alone to fill the tank is:
A. 10
B. 12
C. 14
D. 16

Answer: Option C

Explanation:

Part filled in 2 hours = 2 = 1
6 3

Remaining part = 1 - 1 = 2 .
3 3

(A + B)'s 7 hour's work = 2
3

(A + B)'s 1 hour's work = 2
21

C's 1 hour's work

   = { (A + B + C)'s 1 hour's work } - { (A + B)'s 1 hour's work }

   = 1 - 2 = 1
6 21 14

C alone can fill the tank in 14 hours.