1. Warm Up 3 – 2 Add or subtract. 1 + – 1. 1 2. 1 3. 6.5 + (–1.2) 5.3
3 5
2 5 –
1 5 1 2.
11 12
7 12
1 3 1
3 – 2
(–1.2)
5.3
– 0.9
2.5

2. Adding and Subtracting with Unlike Denominators
Section 2.6

3. Objectives:
Add and subtract fractions by using factoring to find common denominators. (NS 2.2)
Add and subtract rational numbers (NS 1.2)

4. Words to know: Least common
denominator:
least common multiple of the denominators of two or more fractions.

5. To add and subtract fractions with unlike denominators, first find a common denominator using one of these methods:
Method 1 Find a common denominator by multiplying the denominators.
Method 2 Find the least common denominator
(LCD).

6. Adding Fractions – using common denominator
Use 6 x 9 as the common denominator.
Add numerators
Simplify

7. Let’s review…
Do you remember how to find Least Common Multiple?
12 – 12, 24, 36, 48, 60, 72, 84, 96, 108
20 – 20, 40, 60, 80, 100, 120
LCD = 60

8. How do you find the Least Common Multiple?

9. Adding Fractions – using LCM
The LCM of 6 and
9 is 18.
Add numerators.
Simplify fraction.

10. Evaluating Algebraic Expressions
Evaluate the expression x – y + z when
The LCM of 2, 4, and 8 is 8.
Simplify
Add numerators

11. One more option…. ● 3 ● 3 ● 4 ● 4 20 = 24 9 = 24 The LCM is 24!
What number can you multiply each denominator by to get to 24?
Multiply that number on the top too!
● 3

12. Try on your own…. 1. 3. 2. 4.

13. Application – – , or 12 – 6 – 4 27 4 There will be foot left.
Fred and Jose are building a tree house. They need to cut a 6 foot piece of wood and a foot piece of wood from a 12 foot board. How much of the board will be left?
3 4
5 12
12 – 6 – 4
3 4
5 12
27 4
53 12
12 1 – =
81 12
144 12 –
53 12 =
, or
5 6
10 12 =
There will be foot left.
5 6

14. How do you add or subtract fractions with unlike denominator

15. Lesson Quiz 7 8 1 1. 2. – 3. 4. Evaluate – n for n = . 2 in. + –2 + –2
Add or subtract. 12 1.
5 14
1 7 +
2 3 12 7
1 6 2. 8 – 1 –2
1 15 3.
3 5
2 3 + –2 38
9 16
13 16
4. Evaluate – n for n = . 1 12
3 4
Robert is 5 feet 6 inches tall. Judy is 5 feet 3 inches tall. How much taller is Robert than Judy?
2 in.
3 4