A store advertises that during its Labor Day sale $15 will be deducted from every purchase over $100. In addition, after the deduction is taken, the store offers an early-bird discount of 20% to any person who makes a purchase before 10 a.m. If Hakeem makes a purchase of x dollars,
x > 100, at 8 a.m., what, in terms of x, is the cost of Hakeemís purchase?
(1) 0.20x - 15 (3) 0.85x - 20
(2) 0.20x -3 (4) 0.80x - 12...This is the answer.
I understand the situation in the question. The correct answer is highlighted in red. I selected choice (1) given the fact that Hakeem purchased an item over $100 and that the store offers a discount of $15 and an additional discount of 20%.
It made sense to easily come up with 0.20x - 15. In fact, I also decided to let C = cost and then went on to develop the equation C = 0.20x - 15.
Why is choice (4) correct and my answer incorrect?