9514 1404 393
Answer:
Explanation:
Often, you can work these problems in your head.
If you sold all cookies, your revenue would have been 27×3 = 81. It was 129-81 = 48 more than that. Each muffin generates 4 more revenue than a cookie dies, so there must have been 48/4 = 12 muffins. The 27-12 = 15 were cookies.
You sold 15 cookies and 12 muffins.
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If you let a variable represent the most expensive item (m for muffins), then you can write an equation for the revenue. You may recognize that some of the steps in the solution match the "verbal" solution above.
3(27 -m) +7m = 129
4m +81 = 129
4m = 129 -81 = 48
m = 48/4 = 12 . . . muffins
27-12 = 15 . . . cookies