There has been successive increases of 30% and then 20% in the price of gas from the previous month. By what percentage should a driver reduce gas consumption so that the expenditure does not change?  Choices:
A) 20 % B) 24 % C) 28 % D) 32 % E) 36 %

Rationale: "let p be the original price per unit of gas . let x be the original gas consumption . let y be the reduced gas consumption . y * 1.2 * 1.3 * p = x * p y = x / ( 1.2 * 1.3 ) which is about 0.64 x which is a decrease of about 36 % . the answer is e ."
Answer: E