Problem: a couple who own an appliance store discover that if they advertise a sales discount of 10 % on every item in the store , at the end of one month the number of total items sold increases 10 % . their gross income from sales for one month decreases by what percent ?
Rationale: "let p be the original price and let x be the number of items sold originally . the original income is p * x . after the changes , the income is 0.9 p * 1.1 x = 0.99 * ( p * x ) , a decrease of 1 % . the answer is a ."
annotated_formula: subtract(subtract(10, 10), divide(10, 10))