Mrs. whitney is baking fifteen dozen cookies for a charity bake sale. her recipe requires one cup of butter for every thirty-six cookies. how many cups of butter will she use in all?

First we know that a dozen is 12

so She makes 12×15 cookoes which is

180 cookies

so lets put it in an equation.

36 cookies = 1 cup butter

180 cookies = X

The criss cross method

36 X = 180 cup of butter (notice here that the cookie cancelled out)

dividing each side by 36 we get

5 cups of butter