There has been successive increases of 15% and then 10% 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?	Options
A) 12% B) 15% C) 18% D) 21% E) 24%
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*1.1*1.15*P = x*P   y = x / (1.1*1.15) which is about 0.79x which is a decrease of about 21%.   The answer is 21%.
<result>D</result>
There has been successive increases of 15% and then 10% 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?