Adding Fractions with Calculators

Fraction calculators free students from the tedium of manually adding and subtracting fractions with unlike denominators. While some practice adding and subtracting fractions with unlike denominators is important, it is more important that students have an understanding of what they are doing. Fraction calculators can be immensely helpful in teaching why common denominators are important.

This activity will walk through how to use the calculators to perform addition and subtraction of fractions with unlike denominators. Students first use the fraction calculator to obtain the answer. They then complete the process for finding common denominators by filling in the blanks in a detailed worksheet.

Math Objective

Conceptual understanding of adding and subtracting fractions with unlike denominators.

Skills/Outcomes
  • adding and subtracting of fractions with unlike denominators

Calculator Skills

  • Entering fractions
  • Entering mixed fractions
  • Simplifying fractions if necessary

 

What To Do

Files to Use

Download Info/Instructions

addsubfr.doc

Materials

fraction calculators

worksheets pre-formatted for finding like denominators

Optional Resources

manipulatives: pie charts, fraction bars

 

Classroom Discussion and Activities

Added Exercises

 

Classroom Discussion and Activities

Teacher Note: We assume that you have introduced the idea of adding and subtracting fractions with unlike denominators using simple examples. We also assume that you have taught the algorithm for finding common denominators (i.e., multiplying each fraction by one that is equivalent to one).

 

 
In the first step, students will estimate their answers. We recommend that you use number lines as a basis for estimating the answer. Be sure to discuss reasonable answers here, and do not require students to come up with exact fractions. Estimates will encourage students to give reasons for their answers, and a visual aide such as a number line should help.

 

 
This will require some facility with fractions calculators. Make sure that they enter the numbers for the fractions correctly.

 

 
Explain to students how the denominator in the answer is the common denominator for each of the two fractions being subtracted. Be sure to emphasize that students are working with fractions with unlike denominators.

 

 
Ask the students what they multiply 4 by to get 12. Then stress the notion of equivalence. Fractions have to be equivalent. So, the fractions in the brackets must be equal to one. Then work through the answer.

 

You can finish the exercise by comparing the answer with the visual representation that the students drew in Step 1.

Added Exercises

This same process of finding the answer and then figuring out the process can be used on addition / subtraction of mixed numeral, improper fractions, and fractions which need to be simplified. A template for these problems can be found in the file addsubfr.doc. You can change the problems simply by going through each step and changing the fractions and the signs. This is an easy way to create multiple problems for practice in class.

For answers which need to be simplified, have students write both the non simplified and simplified answers.