Fractions In The Kitchen

As a student, I remember being able to connect math to the real world because I took Home Economics. In Home Economics, we baked cakes, cookies, rice crispy treats, and pies. In order to prepare the baked goods with accuracy we had to measure out ingredients according to the number of people we served. For example, if a Carrot Cake recipe called for the following ingredients and served 18 but we need to serve a class of 24 we would have to use a little bit of math to adjust the ingredients and not take away from the taste and consistency of the cake itself. We no longer have Home Economics in our school and I find that many of my students struggle with measurement. Parents, if you have time to bake with your kids it will help tremendously with connecting fractions to the real world. My students have a hard time with fractions and it may be because home economics was removed from our school and they probably don't spend anytime in the kitchen.

Recipe for Carrot Cake (18 Servings):

* 4 eggs
* 1 1/4 cups vegetable oil
* 2 cups white sugar
* 2 teaspoons vanilla extract
* 2 cups all-purpose flour
* 2 teaspoons baking soda
* 2 teaspoons baking powder
* 1/2 teaspoon salt
* 2 teaspoons ground cinnamon
* 3 cups grated carrots
* 1 cup chopped pecans
*

* Cream Cheese Frosting
* 1/2 cup butter, softened
* 8 ounces cream cheese, softened
* 4 cups confectioners' sugar
* 1 teaspoon vanilla extract
* 1 cup chopped pecans
* We have to scale a recipe using the following formula:


desired servings
------------------- = conversion factor
original servings

So in this case the desired servings was 24 and the original servings was 18:

24
--- = 1.33
18
Then we have to multiply each ingredient by 1.33 and get the following new measurements:


Carrot Cake Recipe to serve 24:

* 5-1/4 eggs
* 1-2/3 cups vegetable oil
* 2-2/3 cups white sugar
* 2-3/4 teaspoons vanilla extract
* 2-2/3 cups all-purpose flour
* 2-3/4 teaspoons baking soda
* 2-3/4 teaspoons baking powder
* 3/4 teaspoon salt
* 2-3/4 teaspoons ground cinnamon
* 4 cups grated carrots
* 1-1/3 cups chopped pecans
* 2/3 cup butter, softened
* 11 ounces cream cheese, softened
* 5-1/3 cups confectioners' sugar
* 1-1/4 teaspoons vanilla extract
* 1-1/3 cups chopped pecans


To multiply the fractions, for example when we convert 1 1/4 cups of vegetable oil to the new measurement we have to change this mixed number to a decimal: we know 1/4 =.25 because its a common fraction and 1 out of 4 quarters is.25. Therefore, we add the decimal to the whole number 1 +.25 = 1.25. Next we multiply 1.25 times 1.33. which is 1.66. We have to measure in cups so we will change 1.66 to a fraction 1 and 66/100 = 1 and 2/3 cup because 2/3=.66
You multiply 1.33 times the rest of the ingredients.