Question

I sell cookies for $3 and muffins for $7. Yesterday, I made $129. I sold a total of 27 items. How many of each did I sell?

Answer 1

You sold 15 cookies and 12 muffins

Explanation:

So you're given that 1 cookie is sold for $3 and 1 muffin is sold for $7

You're also given that in total you made $129, and sold 27 items

Let's make equations from that, letting c stand for amount of cookies and m for amount of muffins.

• 3c + 7m = 129 (equation for amount of money made)
• c + m = 27 (equation for amount of items sold)

Now we can use the second equation to find m:

c + m = 27

m = 27 - c

Not we can substitute m into the first equation to find c:

3c + 7m = 129

3c + 7(27-c) = 129 [substitute m for (27-c)]

3c + 189 -7c = 129 [distribute 7 into (27-c)]

-4c + 189 = 129 [combine like terms]

-4c = -60 [subtract 189 from both sides]

c = 15 [divide both sides by -4]

Now we can substitute c into the second equation to find m:

c + m = 27

15 + m = 27

m = 12

Answer 2

You sold 15 cookies and 12 muffins.

c - cookies
m - muffins

c + m = 27

3c + 7m = 129

I don’t know how to explain how to do efficiently but I just plugged in numbers until it worked:

3(15) + 7(12) = 129

45 + 84 = 129