Lesson: Add and Subtract Mixed Numbers

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Lesson Objective

SWBAT add and subtract mixed numbers with unlike denominators by finding common denominators.

Lesson Plan


State Standard:


Standard Name:

Add & Subtract Fractions


SWBAT add and subtract mixed numbers with unlike denominators by finding common denominators.

Essential Question:

How can I compare numbers that do not all look the same?


Word Wall Words:

Fraction, add

Do Now:

Add 5 fractions with like denominators.



We’ve used our fraction bars to add and subtract fractions with unlike denominators, but what do we do when we don’t have our fraction bars handy?

Direct Instruction:

To add or subtract fractions with unlike denominators, rename them as fractions with a common denominator. Let’s try it when adding ½ and ¼. First, I want to find the LCM of the denominators to have a common denominator. I know that the LCM is 4. Now I need to write equivalent fractions that have 4 in the denominator. ¼ already has a 4 so I just need to change ½. TO get from 2 to 4, I multiplied by 2 in the denominator, so I must multiply by 2 in the numerator. My new equivalent fraction is 2/4. ¼ plus 2/4 gives me ¾. If you can simplify, you must!

Model again with 5/6-3/4.

Guided Practice:

We will work the first few problems on your handout together.

Independent Practice:

Now you will complete the remainder of your assignment. Use common denominators to find your answers. You may use your fraction bars to check your work if you are stuck.

Math Journals:

How is a common denominator helpful? How does it relate to the LCM?


Exit Slip: 1. ¾ +5/6

2. 6/7 – 3/8

Center Options:

Center 1: pratice on different forms of fractions

Center 2: Extra pratice on skip counting

Center 3: adding fractions with like & unlike denominators


Struggling students can continue to work on adding with like denominators and proper fractions.


Advanced students will add 3 fractions with uncommon denominators.


Lesson Resources

Add Subtract Mixed Numbers   Classwork


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