OG详解-OG3 数学1 Q21

The correct answer is 1.8. It’s given that the regular price of a shirt at astore  is $11.70 , and the sale price of the shirt is  80%  less than the regular price. It follows that the sale price of the shirt is  $11.70 ( 1−80100​​）, or $11.70(1-0.8), which is equivalent to $2.34 . It’s also given that the sale price of the shirt is  30% greater than the store’s cost for the shirt. Let x represent the store’s cost for the shirt. It follows that 2.34 = (1+3​0100​ ) x, or 2.34 = 1.3x. Dividing both sides of this equation by 1.3 yields x = 1.80. Therefore, the store’s cost, in dollars, for the shirt is 1.80. Note that 1.8 and 9/5 are examples of ways to enter a correct answer.