On increasing the price of T.V. sets by 70%, their sale decreases by 20%. What is the effect on the revenue receipts of the shop ? Choose the correct answer.
A) 4 B) 5 C) 36 D) 2 E) 7

Rationale: "explanation : let the price be = rs . 100 , and number of units sold = 100 then , sale value = rs . ( 100 × 100 ) = rs . 10000 new sale value = rs . ( 170 × 80 ) = rs . 13600 increase % = 3600 / 10000 × 100 = 36 % answer : c"
Answer: C