CONFIDENTIAL 1
Today we will review “Multiplying & Dividing Fractions”
CONFIDENTIAL 2
Let’s Warm up:.
1) ¾ + ¼ = 2) 3/5 – 1/4 =
3) 5/6 – 2/5 = 4) ½ + ¾ - ¼ =
CONFIDENTIAL 3
Estimating Products
Estimate using Compatible Numbers These are numbers that are easy to divide mentally Estimate ¼ x 13 ¼ x 13 means ¼ of 13 Find a number close to13 that is a multiple of 4. ¼ x 13 ¼ x 12 ¼ x 12 = 3 So, ¼ x 13 is about 3.
12 and 4 are compatible numbers since 12 ÷ 4 = 3
12 ÷ 4 = 3
CONFIDENTIAL 4
Estimating Products
Your Turn! Estimate 2/5 x 11
CONFIDENTIAL 5
Estimating Products
Estimate by Rounding to 0, ½, or 1. Estimate 1/3 x 7/8
1/3 x 7/8 ½ x 1 ½ x 1 = ½ So, 1/3 x 7/8 is about ½.
0 1/2 1
1/3 7/8
1/3 is about 1/2 7/8 is about 1
CONFIDENTIAL 6
Estimating Products
Your Turn! Estimate 5/8 x 9/10
CONFIDENTIAL 7
Estimating Products
Estimating with Mixed Numbers 11 ¾ x 8 1/6 Round each number to the nearest whole number 11 ¾ x 8 1/6 12 x 8 = 96
Round 11 ¾ to 12 Round 8 1/6 to 8
CONFIDENTIAL 8
Multiplying Fractions
To multiply fractions, multiply the numerators and multiply the denominators a x c = a x c
b d b x d where b and d are not 0 2 x 1 = 2 x 1 = 2
5 2 5 x 2 10
CONFIDENTIAL 9
Multiplying Fractions
Your Turn Find 1/3 x 1/4
CONFIDENTIAL 10
Multiplying Fractions
Multiplying Fractions and Whole Numbers First write the whole number as a fraction Example; Find 3/5 x 4 3/5 x 4 = 3/5 x 4/1
= 3 x 4
5 x 1
= 12 or 2 2/5
5
Write 4 as 4/1
Multiply
Simplify
CONFIDENTIAL 11
Multiplying Fractions
Your Turn 2/3 x 6
CONFIDENTIAL 12
Multiplying Fractions
Simplify before Multiplying Find ¾ x 5/6 ¾ x 5/6 = 3 x 5 = 3 x 5
4 x 6 4 x 6
= 5
8
1
2
The numerator 3 and denominator 6
have a common factor 3
Divide both the numerator and the denominator by 3
CONFIDENTIAL 13
Multiplying Fractions
Find 5/6 x 9/10
CONFIDENTIAL 14
Multiplying Fractions
Evaluate Expressions Evaluate ab if a = 2/3 and b = 3/8 ab = 2/3 x 3/8
= 2 x 3
3 x 8
= 1
4
Replace a with 2/3 and b with 3/8
The GCF of 2 and 8 is 2. The GCF of 3 and 3 is 3. Divide both the numerator and denominator
by 2 and then by 3.
1
1
1
4
CONFIDENTIAL 15
Multiplying Fractions
Evaluate 3 c if c = 2
4 5
CONFIDENTIAL 16
Multiplying Mixed Numbers
To multiply mixed numbers, write the mixed numbers as improper fractions
Then multiply as with fractions Find ¼ x 4 4/5
5
11
5
654
2415
24
4
15
44
4
1
Divide 24 and 4 by their GCF, 4
1
4
CONFIDENTIAL 17
Multiplying Mixed Numbers
Your Turn Find 2/3 x 2 1/2
CONFIDENTIAL 18
Multiplying Mixed Numbers
Your Turn Find 2 ½ x 2 ¼
CONFIDENTIAL 19
Dividing Fractions
To divide by a fraction, multiply by its reciprocal
Any two numbers whose product is 1 are called reciprocals. 5 x 1/5 = 1; so the reciprocal of 5 is 1/5
To find the reciprocal of a fraction, invert the fraction. That is, switch the numerator and denominator.
Reciprocal of 2/3 is 3/2
0 d and c,b, where, c
d
b
a
d
c
b
a
CONFIDENTIAL 20
Dividing Fractions
Find 1/8 ÷ 3/4
rs.DenominatoMultiply .numeratorsMultiply 6
1
4 GCF by the 4 and 8 Divide 38
41
3
4 reciprocal by theMultiply
3
4
8
1
4
3
8
1
2
1
CONFIDENTIAL 21
Dividing Fractions
Your Turn Divide ¼ ÷ 3/8
CONFIDENTIAL 22
Dividing Mixed Numbers
1. Write mixed numbers as improper fractions
2. Multiply by the reciprocal
3. Simplify
7
13or
7
22
2 GCF by the 4 and 2 Divide 7
4
2
11
reciprocal by theMultiply 7
4
2
11
fractionsimproper as numbers mixed Write4
7
2
11
4
31
2
15
4
31
2
15 Find
2
1
CONFIDENTIAL 23
Dividing Mixed Numbers
Your Turn Divide. Write in simplest form.
3
12
5
14
CONFIDENTIAL 24
Let’s take a break!
CONFIDENTIAL 25Title: Format: WebEx Web BrowserDouble-click to edit
CONFIDENTIAL 26
Assessment
1. Estimate 1/8 x 15
2. Estimate ¾ x 21
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Assessment
3. Multiply. Write in simplest form. 1/8 x ½
4. Multiply. Write in simplest form. 4/5 x 10
CONFIDENTIAL 28
Assessment
5. Multiply. Write in simplest form.
6. Multiply. Write in simplest form.
8
32
2
1
3
2
2
11
CONFIDENTIAL 29
Assessment
7. Divide. Write in simplest form.
8. Divide. Write in simplest form.
2
1
4
1
3
1
6
5
CONFIDENTIAL 30
Assessment
9. Divide. Write in simplest form.
10. Divide. Write in simplest form.
22
13
7
2
5
13
CONFIDENTIAL 31
Good Job!
You have learned a lot today!!!