On selling 17 balls at Rs. 720, there is a loss equal to the cost price of 5 balls. The cost price of a ball is:

A.    Rs. 45   
B.    Rs. 50
C.    Rs. 55   
D.    Rs. 60
Answer:  D

Explanation:

(C.P. of 17 balls) - (S.P. of 17 balls) = (C.P. of 5 balls)
 C.P. of 12 balls = S.P. of 17 balls = Rs.720.
 C.P. of 1 ball = Rs.(720/12) = Rs. 60.