The Shopkeeper increased the price of a product by 25% so that customer finds it difficult to purchase the required amount. But somehow the customer managed to purchase only 64% of the required amount. What is the net difference in the expenditure on that product? Choose one
A) 12.5 % B) 13 % C) 15 % D) 17 % E) 20 %

Rationale: "quantity x rate = price 1 x 1 = 1 0.64 x 1.25 = 0.8 decrease in price = ( 0.2 / 1 ) × 100 = 20 % e )"
Answer: E