Transcript 2CH4L9 - Groupfusion.net

4-9 Estimate with Fractions
Warm Up
Problem of the Day
Lesson Presentation
Course 2
4-9 Estimate with Fractions
Warm Up
Divide. Write each answer in simplest form.
1. 4 ÷ 3
10
40 or
13 1
3
3
3 ÷ 6
2. 4
5
5
8
3. 15 2 ÷ 5
3 6
94 or
18 4
5
5
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4-9 Estimate with Fractions
Problem of the Day
Fill in the square using the numbers 5–13
so that all sums (rows, columns, and main
diagonals) are the same.
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8
13
6
7
9
11
12
5
10
4-9 Estimate with Fractions
Learn to estimate sums and differences of
fractions and mixed numbers.
Course 2
4-9 Estimate with Fractions
Sometimes, when solving problems, you may
not need an exact answer. To estimate sums
and differences of fractions and mixed
numbers, round each fraction to 0, 1 , or 1.
2
you can use a number line to help.
0
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2
5
1
2
1
4-9 Estimate with Fractions
You can also round fractions by comparing
numerators with denominators.
Guidelines for Rounding Fractions
1
Round to 1 if the
Round to 0 if
Round to
if the
2
numerator is nearly
the numerator
numerator is about
equal to the
is much smaller than
half the denominator.
denominator.
the denominator.
Examples:
1, 3 , 2
9 20 11
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Examples:
2 ,5 ,7
5 12 13
Examples:
8 , 23 , 97
9 25 100
4-9 Insert
Lesson
Title
Here
Estimating
with
Fractions
Additional Example 1: Measurement Application
3
A blue whale can grow to 33 5 m long, while
1
the great white shark may be as long as 4 2 m.
About how much longer is the blue whale?
33 3 – 4 1
2
5
33 3
5
33
33 1
2
1 – 1 = 29
4
2
2
1
4
2
4
1
2
Round each mixed
number.
Subtract.
The blue whale is about 29 m longer.
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4-9 Insert
Lesson
Title
Here
Estimating
with
Fractions
Try This: Example 1
A Cocker Spaniel may grow to weigh about
1
11 2 kilograms while the Chihuahua will not
weigh more than 2 7 kilograms. About how
8
much more can a Cocker Spaniel weigh?
11 1 – 2 7
8
2
11 1
2
11
11 1
2
1 –
3 = 81
2
2
2
7
8
3
Round each mixed
number.
Subtract.
The Cocker Spaniel weighs about 8 1 kg more.
2
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4-9 Estimate with Fractions
Additional Example 2A & 2B: Estimating Sums and
Differences
Estimate each sum or difference.
A. 7 – 1
9
5
7
9
1
1
5
0
Round each fraction.
Subtract.
1–0=1
B. 4 5 + 3 1
9
45
9
8
41
2
1
41+ 3 = 7
2
2
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31
8
3 Round each mixed fraction.
Add.
4-9 Estimate with Fractions
Additional Example 2C: Estimating Sums and
Differences
Estimate the sum.
C. –2 1 +
8
–2 1
8
7
12
–2
1
–2 + 1 = –1
2
2
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7
12
1
2
Round each number.
Add.
4-9 Estimate with Fractions
Try This: Example 2A & 2B
Estimate each sum or difference.
A. 7 – 1
8
6
7
8
1
1
6
0
Round each fraction.
Subtract.
1–0=1
B. 5 3 + 2 2
5
53
5
9
51
2
1
51+ 2 = 7
2
2
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22
9
2 Round each mixed fraction.
Add.
4-9 Estimate with Fractions
Try This: Example 2C
Estimate the sum.
C. –4 2 +
9
–4 2
9
8
15
–4
1
1
=
+
–3
–4
2
2
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8
15
1
2
Round each number.
Add.
4-9 Estimate with Fractions
When exact answers are not needed for
a problem, you can use estimation.
When exact answers are needed, an
estimate can help you decide if your
answer is reasonable.
Helpful Hint
Words like about and around signal that an exact
answer is not necessary.
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4-9 Insert
Lesson
Here
Estimate
with Title
Fractions
Additional Example 3A: Deciding If an Estimate is
Enough
Decide if you need an exact answer or if an
estimate is enough.
A. Michael knows there will be 18 people at his
party. He plans to give each person a 1 2 cup
3
serving of popcorn. If he can buy popcorn in 10cup bags, how many bags should he buy?
Since he will be buying the popcorn in 10 cup bags, an
estimate of the amount will give him enough
information to decide how many bags of popcorn to
buy.
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4-9 Estimate with Fractions
Additional Example 3B: Deciding If an Estimate is
Enough
Decide if you need an exact answer or if an
estimate is enough.
B. For a soccer celebration, Ellis buys rolls for
$5.29 and 3 1 pounds of barbequed ham for
4
$9 per pound. How much does she spend for
the food?
Since the problem is asking for the exact amount
of money she spends, an estimate would not be
appropriate.
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4-9 Insert
Lesson
Here
Estimate
with Title
Fractions
Try This: Example 3A
Decide if you need an exact answer or if an
estimate is enough.
Cynthia has two dogs. Each dog is fed 1 3
4
cups of dog food each day. If she buys a 30
lb bag of dog food, is that enough to last for
three weeks?
Since she is only trying to get an idea of how
long a 30 lb bag of dog food will last, an
estimate should give her enough information to
decide .
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4-9 Insert
Lesson
Here
Estimate
with Title
Fractions
Try This: Example 3B
Decide if you need an exact answer or if an
estimate is enough.
William’s uncle was going on a 14-day
camping trip. He is required to take 1 1 pills
2
of a certain medication each day. How
many pills should he take with him on this
trip?
Since his uncle must take a certain amount of pills
each day for a medical condition, an estimate
would not be appropriate.
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4-9 Estimating
Insert Lesson
with
Title
Fractions
Here
Lesson Quiz
1. The new show arena being built in Franklin County
is 150 3 feet long and 110 1 feet wide. Estimate
4
2
the difference between the length and width. 40 ft
Estimate each sum or difference.
2. 5 + 4 1 1
9
5
2
3. 7 – 3 1
8
7 2
3
1
4. 9 4 – 6 5 4
5. Decide if you need an exact answer or if an
estimate is sufficient. Janet needs 4 1 quarts of oil
2
1
for her car. If she has 2 2 quarts, how much more
does she need? An estimate is sufficient.
Course 2