Course 1 5-7 Multiplying Fractions 5-7 Multiplying Fractions Course 1 Warm Up Warm Up Problem of the Day Problem of the Day Lesson Presentation Lesson Presentation
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Course 1
5-7 Multiplying Fractions5-7 Multiplying Fractions
Course 1
Warm UpWarm Up
Problem of the DayProblem of the Day
Lesson PresentationLesson Presentation
Course 1
5-7 Multiplying Fractions
Warm Up
1. What is of 12?
2. What is of 100?
3. What is of 120?
4. What is of 100?
5. What is of 480?
6
50
60
12__
12__
12__
14 __
14 __
25
120
Course 1
5-7 Multiplying Fractions
Problem of the Day
Your favorite uncle left one-fifth of his estate to each of his three children and the rest to his favorite charity. If his estate was worth $105,000, how much was given to charity?$42,000
Course 1
5-7 Multiplying Fractions
Learn to multiply fractions.
Course 1
5-7 Multiplying Fractions
On average, people spend of their lives asleep. About
of the time they sleep, they dream. What fraction of
a lifetime does a person typically spend dreaming?
1
3__
1
3__
1
4__
1
4__
1
4__ 1
3__
1
4__ 1
3__
• =1
12__
One way to find of is to make a model.
Find of .
Course 1
5-7 Multiplying Fractions
You can also multiply fractions without making a model.
1
4__ 1
3__
• 1 • 1
4 • 3 _____
1
12__
=
=
Multiply the numerators.Multiply the denominators.
A person typically spends of his or her lifetime dreaming.
1
12__ The answer is in simplest
form.
Course 1
5-7 Multiplying Fractions
Additional Example 1A: Multiplying Fractions
Multiply. Write each answer in simplest form.
1
4__ 2
5__• _____=
=
Multiply numerators. Multiply denominators.
2
20__
1 • 2 4 • 5
1
4__ •
2
5__
The GCF of 2 and 20 is 2.
The answer is in simplest form.=1
10__
Course 1
5-7 Multiplying Fractions
Additional Example 1B: Multiplying Fractions
Multiply. Write each answer in simplest form.
5
7__ 4
15__•
_____
=
=
Use the GCF to simplify the fractions before multiplying. The greatest common factor of 5 and 15 is 5.
4
21__
1 • 4
7 • 3
5
7__ •
4
15__
Multiply numerators. Multiply denominators.
The answer is in simplest form.
1
7__ •
4
3__
1
3
=
Course 1
5-7 Multiplying Fractions
Additional Example 1C: Multiplying Fractions
Multiply. Write each answer in simplest form.
4
9__ 6
10__• ______=
=
Multiply numerators. Multiply denominators.
24
90__
4 • 6
9 • 10
4
9__ •
6
10__
The GCF of 24 and 90 is 6.
The answer is in simplest form.=4
15__
Course 1
5-7 Multiplying Fractions
Check It Out: Example 1A
Multiply. Write each answer in simplest form.
1
2__ 3
6__• _____=
=
Multiply numerators. Multiply denominators.
3
12__
1 • 3 2 • 6
1
2__ •
3
6__
The GCF of 3 and 12 is 3.
The answer is in simplest form.=1
4__
Course 1
5-7 Multiplying Fractions
Check It Out: Example 1B
Multiply. Write each answer in simplest form.
3
7__ 5
9__•
_____
=
=
Use the GCF to simplify the fractions before multiplying. The greatest common factor of 3 and 9 is 3.
5
21__
1 • 5
7 • 3
3
7__ •
5
9__
Multiply numerators. Multiply denominators.
The answer is in simplest form.
1
7__ •
5
3__
1
3
=
Course 1
5-7 Multiplying Fractions
Check It Out: Example 1C
Multiply. Write each answer in simplest form.
3
7__ 5
15__• ______=
=
Multiply numerators. Multiply denominators.
15105____
3 • 5 7 • 15
3
7__ •
5
15__
The GCF of 15 and 105 is 15.
The answer is in simplest form.=1
7__
Course 1
5-7 Multiplying Fractions
Additional Example 2A: Evaluating Fraction Expressions
2
5__
1
3__ b •
2
5__
2
5__1
3__ •
_____1 • 23 • 5
2
15__
Substitute for b.1
3__
Multiply.
The answer is in simplest form.
b =
Evaluate the expression b • for each value of b.
Write each answer in simplest form.
Course 1
5-7 Multiplying Fractions
You can look for a common factor in a numerator and a denominator to determine whether you can simplify before multiplying.
Helpful Hint
Course 1
5-7 Multiplying Fractions
Additional Example 2B: Evaluating Fraction Expressions
b = 3
8__
b •2
5
__
2
5
__3
8
__ •
_____3 • 14 • 5
3
20
__
Substitute for b.3
8__
Use the GCF to simplify.
The answer is in simplest form.
1
4
2
5
__3
8
__ •
Multiply.
Course 1
5-7 Multiplying Fractions
Additional Example 2C: Evaluating Fraction Expressions
b = 5
7__ b •
2
5__
2
5__5
7__ •
_____5 • 27 • 5
10
35__
Substitute for b.5
7__
Multiply.
The GCF of 10 and 35 is 5.
The answer is in simplest form.2
7__
Course 1
5-7 Multiplying Fractions
Check It Out: Example 2A
Evaluate the expression c • for each value of c.
Write each answer in simplest form.
c =
1
4__
1
7__ c •
1
4__
1
4__1
7__ •
_____1 • 17 • 4
1
28__
Substitute for c.1
7__
Multiply.
The answer is in simplest form.
Course 1
5-7 Multiplying Fractions
Check It Out: Example 2B
c = 2
7__ c •
1
4
__
1
4
__2
7
__ •
_____1 • 17 • 2
1
14
__
Substitute for c.2
7__
Use the GCF to simplify.
The answer is in simplest form.
1
2
1
4
__2
7
__ •
Multiply.
Course 1
5-7 Multiplying Fractions
Check It Out: Example 2C
c = 4
7__ c •
1
4__
1
4__4
7__ •
_____4 • 17 • 4
4
28__
Substitute for c.4
7__
Multiply.
The GCF of 4 and 28 is 4.
The answer is in simplest form.1
7__
Course 1
5-7 Multiplying Fractions
Lesson Quiz
Multiply. Write each answer in simplest form.
1. 2.
Evaluate the expression x • for each value of
x. Write the answer in simplest form.
3. x = 4. x =
5. At a particular college of the students take a
math class. Of these students, take basic algebra.
What fraction of all students take basic algebra?
3
5__1
4__ •
5
7__3
10__ •
1
8__
4
5__ 1
8__
2
5__
1
4__
3
20__ 3
14__
1
10__ 1
64__
1
10__
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