1. Aim: How do we find a common denominator between two fractions?
October 29, Math 201
Objective: Students will add and subtract fractions with unlike denominators.
Aim: How do we find a common denominator between two fractions?
NYS Mathematics Standards: 6.N.16
Prior Knowlege: Find equivalent fractions for

2. Mini-lesson: Fractions that have the same number in their denominator are called like fractions.
When we add and subtract fractions, they must be like fractions.
Which of the following pairs of fractions are like fractions?

3. If a pair of fractions are not like fractions, what do you think they are called?
You can replace unlike fractions with equivalent fractions that have the same denominator. This is called finding a common denominator.
A common denominator of two or more fractions is a common multiple of the denominators.

4. Let’s find some common multiples!
Example: Find the first 10 multiples for 3 and 4:
M3 = 3, 6, 9, 12, 15, 18, 21, 24, 27, 30
M4 = 4, 8, 12, 16, 20, 24, 28, 32, 36, 40
What multiples do they have in common?
What do you suppose is the Least Common Multiple between them?
We can use the Least Common Multiple for the lowest common denominator!

5. Find equivalent fractions with the same denominator using the LCM
(What does that stand for?)
M9 =
M6 =

6. Guided Practice:
So now let’s make equivalent fractions for our fraction pair:

7. Now let’s add them:

8. Independent Practice:
Step 1: Find the least common multiple to use as your lowest common denominator
Step 2: Make equivalent fractions for each with the common denominator
Step 3: Add the fractions by adding the numerators and keeping the same denominator

9. What do we call fractions with different denominators
To find the lowest common denominator, we find the ____________________
What kind of fractions do we make with our common denominator?___________________
What kind of fractions can we add?__________
Homework: