On selling 15 balls at Rs. 720, there is a loss equal to the cost price of 5 balls. The cost price of a ball is:  Select
A) s . 45
B) s . 50
C) s . 55
D) s . 60
E) s . 72

Rationale: "( c . p . of 15 balls ) - ( s . p . of 15 balls ) = ( c . p . of 5 balls ) c . p . of 10 balls = s . p . of 15 balls = rs . 720 . c . p . of 1 ball = rs . 720 / 10 = rs . 72 . answer : option e"
Answer: E