Converting Fractions

It is common to have students learn about fractions through pie diagrams and then shift quickly into manipulating symbols. Research indicates that students need to visualize fractions in different ways in order to get a deeper understanding of what fractional concepts are all about. Even pie diagrams can be inadequate.

This lesson uses cooking as a common backdrop for practice in estimating, converting, and visualizing fractions using both pie diagrams and measuring utensils such as cups and tablespoons. The link between two different types of representations is important if students are to achieve a better understanding of fractional quantities.

Math Objective

Estimate, convert, and represent different fractional quantities.

Skills/Outcomes
  • Estimate quantities
  • Multiply or divide fractions based on original quantities using fraction calculators
  • Convert mixed fractions to improper fractions and back again

 

What To Do

Files to Use

Download Info/Instructions

recipe.doc

Materials

fraction calculators

 

Classroom Discussion and Activities

Teacher Note: Make up your own recipe using relatively easy fractions for practice. Also, you can copy and paste images in recipe.doc to make more circles and cups or table/teaspoons if your lesson requires it.

 

This exercise will enable students to practice making the calculations involved in converting a recipe. Make sure the recipe that you use for this exercise involves fractions that are not too difficult. Decide if you are going to expand the recipe (double or triple it) or cut it into a smaller portion (e.g., cut it in half).

 
Introduce this exercise by discussing the problem of wanting to make a larger or smaller amount than the recipe calls for. Chocolate chip cookies are a good example. If you want to double the number of cookies, you must have twice as much of everything in the recipe. The amount needed is fairly obvious if the recipe calls for 1 cup of butter, but it isn't so obvious if the original recipe calls for 2 1/4 cups of flour.

 

 

Begin with one of the original fractional quantities. Have students represent that quantity using a pie diagram or describe "what it's close to." For example, 3/8 is close to 1/2. Continue the discussion to get an estimate of the new quantity.

 

 

Be sure you are familiar with entering and converting fractions using fraction calculators.

 

 

This is a key step. Be sure to discuss the common features between the fractional portion represented in the pie diagram and how it is represented in cups or table/teaspoons. This step may require separate instruction on representing simple quantities using the cups or table/teaspoons.