5-7 adding and subtracting with unlike denominators course 1 warm up warm up lesson presentation...
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5-7 Adding and Subtracting with Unlike Denominators
Course 1
Warm Up
Lesson Presentation
Problem of the Day
Course 1
5-7 Adding and Subtracting with Unlike Denominators
Warm UpAdd. Write each answer in simplest form.
1. + 2. +
3. + 4. +
17__ 1
7__ 8
15__ 3
15__
79__ 2
9__ 11
20__ 4
20__
27__ 11
15__
134__
Problem of the Day
If it takes 12 minutes to cut a pipe into three pieces, how long would it take to cut the pipe into four pieces.18 minutes
Course 1
5-7 Adding and Subtracting with Unlike Denominators
Learn to add and subtract fractions with unlike denominators.
Course 1
5-7 Adding and Subtracting with Unlike Denominators
Vocabulary
least common denominator (LCD)
Insert Lesson Title Here
Course 1
5-7 Adding and Subtracting with Unlike Denominators
The Pacific Ocean covers of Earth’s surface. The Atlantic
Ocean covers of Earth’s surface. To find the fraction of the
Earth’s surface that is covered by both oceans, you can add
and , which are unlike fractions.
1
3__
1
3__
1
5__
1
5__
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5-7 Adding and Subtracting with Unlike Denominators
Fractions that represent the same value are equivalent.
Remember!
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5-7 Adding and Subtracting with Unlike Denominators
To add or subtract unlike fractions, first rewrite them as equivalent fractions with a common denominator.
Additional Example 1: Cooking ApplicationMark made a pizza with pepperoni covering of the
pizza and onions covering another . What fraction of
the pizza is covered by pepperoni or onions?
1
4__
1
3__
1
4__
1
4__
1
3__
_____+ Find a common denominator for 4 and 3.
Course 1
5-7 Adding and Subtracting with Unlike Denominators
?
1
4__ 1
3__
1
4__ 1
3__Add +
Additional Example 1 Continued
Write equivalent fractions with 12 as the common denominator.
1
4__
1
3__
_______+
3
12__
4
12__
_____Add the numerators. Keep the common denominator.
1
4__ 1
3__
7
12__
112
112
112
112
112
112
112
The pepperoni or onions cover of the pizza.7
12__
Course 1
5-7 Adding and Subtracting with Unlike Denominators
Try This: Example 1Tori made a pizza with peppers covering of the
pizza and ham covering another . What
fraction of the pizza is covered by ham or peppers?
1
3__
1
2__
1
3__ 1
2__
?1
3__
1
2__
_____+ Find a common denominator for 3 and 2.
Course 1
5-7 Adding and Subtracting with Unlike Denominators
1
3__ 1
2__Add +
Try This: Example 1 Continued
Write equivalent fractions with 6 as the common denominator.
1
3__
1
2__
_______+
2
6__
3
6__
_____Add the numerators. Keep the common denominator.
5
6__
1
3__ 1
2__
16
16
16
16
16
The peppers or ham cover of the pizza.5
6__
Course 1
5-7 Adding and Subtracting with Unlike Denominators
You can use any common denominator or the least common denominator to add and subtract unlike fractions. The least common denominator (LCD) is the least common multiple of the denominators.
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5-7 Adding and Subtracting with Unlike Denominators
Additional Example 2A: Adding and Subtracting Unlike Fractions
Add or Subtract. Write each answer in simplest form.
Method 1: Multiplying denominators.
A. – 7
10__ 3
8__
–7
10__ 3
8__
–56
80__ 30
80__
Multiply the denominators. 10 • 8 = 80
Write equivalent fractions.
Subtract.
Write the answer in simplest form.
26
80__
13
40__
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5-7 Adding and Subtracting with Unlike Denominators
Additional Example 2B: Adding and Subtracting Unlike Fractions
Add or Subtract. Write each answer in simplest form.
Method 2: Use the LCD.
B. – 11
12__ 3
8__
–11
12__ 3
8__
–22
24__ 9
24__
The LCD is 24.
Write equivalent fractions.
Subtract. 13
24__
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5-7 Adding and Subtracting with Unlike Denominators
Additional Example 2C: Adding and Subtracting Unlike Fractions
Add or Subtract. Write each answer in simplest form.
Method 3: Use mental math.
C. + 5
16__ 1
8__
+5
16__ 1
8__
+5
16__ 2
16__
Think: 16 is a multiple of 8, so the LCD is 16.
Rewrite with a denominator of 16.
Add. 7
16__
1
8__
Course 1
5-7 Adding and Subtracting with Unlike Denominators
Additional Example 2D: Adding and Subtracting Unlike Fractions
Add or Subtract. Write each answer in simplest form.
Method 3: Use mental math.
D. – 5
16__ 1
8__
–5
16__ 1
8__
–5
16__ 2
16__
Think: 16 is a multiple of 8, so the LCD is 16.
Rewrite with a denominator of 16.
Subtract. 3
16__
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5-7 Adding and Subtracting with Unlike Denominators
1
8__
Try This: Example 2AAdd or Subtract. Write each answer in simplest form.
Method 1: Multiplying denominators.
A. – 8
10__ 2
6__
–8
10__ 2
6__
–48
60__ 20
60__
Multiply the denominators. 10 • 6 = 60 Write equivalent fractions.
Subtract.
Write the answer in simplest form.
28
60__
7
15__
Course 1
5-7 Adding and Subtracting with Unlike Denominators
Try This: Example 2BAdd or Subtract. Write each answer in simplest form.
Method 2: Use the LCD.
B. – 4
7__ 1
3__
–4
7__ 1
3__
–12
21__ 7
21__
The LCD is 21.
Write equivalent fractions.
Subtract. 5
21__
Course 1
5-7 Adding and Subtracting with Unlike Denominators
Try This: Example 2C Add or Subtract. Write each answer in simplest form.
Method 3: Use mental math.
C. + 3
12__ 1
6__
+3
12__ 1
6__
+3
12__ 2
12__
Think: 12 is a multiple of 6, so the LCD is 12.
Rewrite with a denominator of 12.
Add. 5
12__
1
6__
Course 1
5-7 Adding and Subtracting with Unlike Denominators
Try This: Example 2D Add or Subtract. Write each answer in simplest form.
Method 3: Use mental math.
D. – 3
12__ 1
6__
–3
12__ 1
6__
–3
12__ 2
12__
Think: 12 is a multiple of 6, so the LCD is 12.
Rewrite with a denominator of 12.
Subtract. 1
12__
1
6__
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5-7 Adding and Subtracting with Unlike Denominators
Lesson Quiz
Add or Subtract. Write each answer in simplest form.
1. + 2. –
3. – 4. +
5. Bonnie is making oatmeal bars and the recipes calls for
cup of brown sugar. If she has cup of brown sugar, how
much more does she need?
Insert Lesson Title Here
3
8__ 1
6__ 1
2__ 1
8__
5
12__ 1
6__ 1
6__ 1
8__
3
4__
1
3__
13
24__ 3
8__
1
4__ 7
24__
5
12__ cup
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5-7 Adding and Subtracting with Unlike Denominators