Question

Which two equations could be used to calculate a sale of 15% off your entire purchase?

1) c + 0.15c

2) c + 0.15

3) c - 0.15c

5) c - 0.15

6) 0.85c

7) 1.15c

Answer 1

3 and 6

Explanation:

1) does not work because you are looking for a sale, not a increase of price.

2 also does not work because you are adding 0.15 to the whole price, when you are looking for a sale.

3 does work because you are looking for a discount of 15% for the whole sale. 0.15c = 15% of c. So now you subtract 0.15c from the whole. This shows that this works.

Now that we have one answer we can find the others by seeing if they are equal to c - 0.15c.

We can rule out 5 because c - 0.15 ≠ c - 0.15c.

6 does work because c -0.15c = 0.85c

0.85c = 0.85c

We do not have to check the others now that we have our two answers. Your answer is 3 and 6.