1. ## Find the Cost

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 Hakeem’s purchase?

(1) 0.20x - 15 (3) 0.85x - 20
(2) 0.20x -3 (4) 0.80x - 12...This is the answer.

MY Work:

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?

2. Originally Posted by magentarita
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 Hakeem’s purchase?

(1) 0.20x - 15 (3) 0.85x - 20
(2) 0.20x -3 (4) 0.80x - 12...This is the answer.

MY Work:

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?
You've subtracted the 20% discount before the $15 deduction. The 20% discounted is subtracted after the$15 deduction.

(x - 15) - 20% of (x - 15) = $x - 15 - \frac{1}{5} \, (x - 15) = x - 15 - \frac{x}{5} + 3 = \frac{4}{5} x - 12$.

3. ## I see...

Originally Posted by mr fantastic
You've subtracted the 20% discount before the $15 deduction. The 20% discounted is subtracted after the$15 deduction.

(x - 15) - 20% of (x - 15) = $x - 15 - \frac{1}{5} \, (x - 15) = x - 15 - \frac{x}{5} + 3 = \frac{4}{5} x - 12$.
I did not keep the order.

Got it.