The marked price of a book is 20% more than the cost price. After the book is sold, the vendor realizes that he had wrongly raised the cost price by a margin of 25%. If the marked price of the book is Rs.30, what is the original cost price of the book?
Choose the correct choice from the following choices.
A) rs . 30	B) rs . 25	C) rs . 45	D) rs . 20	E) rs . 10

Rationale: let the incorrect cost price be c 1 and let the original cost price be c 2 . marked price of book is rs . 30 . it is 20 % more than c 1 . therefore , ( 120 / 100 ) x c 1 = 30 or c 1 = 25 . c 1 is more than c 2 margin of 25 % . or c 1 = ( 125 / 100 ) c 2 therefore , c 2 = ( 100 / 125 ) x 25 = rs 20 answer : d
Answer: D