Question

Rina recipe uses 2 cups of sugar to make 2 1/2 dozen cookies. Jonah's recipe uses 2 1/4 cups of sugar to make 3 dozens cookies. Which recipe use more sugar for a dozen cookies? Why?

Answer 1

Let's calculate the "cups of sugar per dozen cookies" ratio:

2 cups
---------- = 0.8 (Rina)
2.5

2.25 cups
------------- = 0.75 (Jonah)
3

Rina uses more sugar for a dozen cookies.

The key here is to "compare unit rates."

Answer 2

Rina's recipe

Explanation:

Rina's recipe

• Cups of sugar: 2 cups

• Cookies: 2 1/2 dozen cookies = 2.5 dozen cookies

Rina uses 2 cups of sugar for 2.5 dozen cookies, which is equal to 2/2.5 = 0.8 cups of sugar per dozen of cookies.

Jonah's recipe

• Cups of sugar: 2 1/4 cups = 2.25 cups

• Cookies: 3 dozen cookies

Jonah uses 2.25 cups of sugar fro 3 dozen cookies, which is equal to 2.25/3 = 0.75 cups of sugar per dozen of cookies.

Rina's recipe uses more cups of sugar per dozen of cookies (0.8 vs. 0.75).