# Adding%20and%20Subtracting%20with%20%20%20%20%20%20Unlike%20Denominators - PowerPoint PPT Presentation

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### Adding and Subtracting with Unlike Denominators 3.5 Warm Up Vocabulary Example: Adding and Subtracting Fractions with Unlike Denominators Example: Adding and ... – PowerPoint PPT presentation

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1
Denominators
• 3.5

2
Warm Up
2 5
3 5
1.
1
7 12
11 12
2.
3 2
3. 6.5 1.2
5.3
4. 3.4 0.9
2.5
3
Learn to add and subtract fractions with unlike
denominators.
4
Vocabulary
least common denominator (LCD)
5
1 3
A pattern for a double-circle skirt requires 9
yards of 45-inch-wide material. To add a ruffle
takes another 2 yards. If the total amount of
material for the skirt and ruffle are cut from a
bolt of fabric 15 yards long, how much fabric
is left?

2 5
1 2
6
To solve this problem, add and subtract rational
numbers with unlike denominators. First find a
common denominator using one of the following
methods
Method 1 Find a common denominator by
multiplying one denominator by the other
denominator.
Method 2 Find the least common denominator
(LCD) the least common multiple of the
denominators.
7
Example Adding and Subtracting Fractions with
Unlike Denominators
Find a common denominator 8(7)56.
2 7
1 8
A.

Multiply by fractions equal to 1.
Rewrite with a common denominator. Simplify
8
Example Adding and Subtracting Fractions with
Unlike Denominators
Write as an improper fraction.
1 6
5 8
B.
1

List the multiples of each denominator and find
the LCD
Multiply by fractions equal to 1.
Rewrite with a common denominator.
Simplify.
9
Try This
Find a common denominator 3(8)24.
5 8
1 3

A.

Multiply by fractions equal to 1.
Rewrite with a common denominator.
10
Try This
Write as an improper fraction.
1 6
3 4
B.
2

List the multiples of each denominator and find
the LCD
Multiply by fractions equal to 1.
Rewrite with a common denominator.
Simplify.
11
Example Evaluating Expressions with Rational
Numbers
4 5
5 6
Evaluate t for t .
Multiply by fractions equal to 1.
Rewrite with a common denominator 6(5) 30.
12
Try This
5 9
7 12
Evaluate h for h .
Multiply by fractions equal to 1.
Rewrite with lowest common denominator (36).
Simplify.
13
Example Consumer Application
Subtract both amounts from 36 to find the amount
of ribbon left.
Write as improper fractions. The LCD is 8.
Rewrite with a common denominator.
Simplify.
14
Try This
Subtract both amounts from 12 to find the amount
of board left.
Write as improper fractions. The LCD is 12.
Rewrite with a common denominator.
Simplify.
15
Lesson Quiz Part 1
5 14
1 7
1.

12
2 3

2.
8
1
3 5
2 3
3.
2

38
9 16
4. Evaluate n for n .
1
16
Lesson Quiz Part 2
12
Robert is 5 feet 6 inches tall. Judy is 5 feet
3 inches tall. How much taller is Robert than
Judy?
5.
3 4