11/15/10
Estimate with Decimals
Entry Task
Today’s Plan:
-Conversions to memorize
-Order Decimals
-Estimate with decimals
Learning Target:
-I can convert, compare, and order fractions and
decimals. I can estimate with decimals.
11/15/10
Estimate with Decimals
Conversions to Memorize
Number your paper from 1-14 for a practice test.
Today’s Plan:
-Conversions to memorize
-Order Decimals
-Estimate with decimals
Learning Target:
-I can convert, compare, and order fractions and
decimals. I can estimate with decimals.
11/15/10
Estimate with Decimals
Change each decimal to a fraction in lowest
terms, and each fraction to a decimal.
6. 0.8 =
1. 0.3 =
1=
11.
10
2. 0.25 =
7. 0.75 =
3. 0.7 =
8. 0.5 =
4. 0.9 =
9. 2 =
5. 0.3 =
3 =
10. 5
12.
1
=
4
13.
2
=
5
3
Today’s Plan:
-Conversions to memorize
-Order Decimals
-Estimate with decimals
14. 1 =
2
Learning Target:
-I can convert, compare, and order fractions and
decimals. I can estimate with decimals.
11/15/10
Estimate with Decimals
Write your name on the upper left hand
corner of the blank side.
Then fold your paper into fourths.
Today’s Plan:
-Conversions to memorize
-Order Decimals
-Estimate with decimals
Learning Target:
-I can convert, compare, and order fractions and
decimals. I can estimate with decimals.
11/15/10
Estimate with Decimals
Human Number Line: Order Decimals
Today’s Plan:
-Conversions to memorize
-Order Decimals
-Estimate with decimals
Learning Target:
-I can convert, compare, and order fractions and
decimals. I can estimate with decimals.
4-1 Estimate with decimals
Learn to estimate decimal sums, differences,
products, and quotients.
Course 2
4-1 Estimate with Decimals
Jessie earned $27.00 for baby-sitting. She wants to use the
money to buy a ticket to a water park for $14.75 and a
souvenir T-shirt for $13.20.
To find out if Jessie has enough money to buy both items, you
can use estimation. To estimate the total cost of the ticket and
the T-shirt, round each price to the nearest dollar, or integer.
Then add the rounded values.
Course 2
4-1 Estimate
Insert Lesson
Title Here
with Decimals
$14.757
7 > 5, so round to $15
$15
$13.202
2 < 5, so round to $13
+ $13
$28
The estimated cost is $28, so Jessie does
not have enough money to buy both items.
To estimate decimal sums and differences,
round each decimal to the nearest integer
and then add or subtract.
Course 2
4-1 Insert
Lesson
Here
Estimate
with Title
Decimals
Remember!
To round to the nearest integer, look at the digit
in the tenths place. If it is greater than or equal
to 5, round to the next integer. If it is less than
5, keep the same integer.
Course 2
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Additional Example 1A: Estimating Sums and
Differences of Decimals
Estimate by rounding to the nearest integer.
A. 4.5 + 8.9
4.5
+8.9
Course 2
5
5 ≥ 5, so round to 5.
+9
14
9 > 5, so round to 9.
Estimate
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Additional Example 1B: Estimating Sums and
Differences of Decimals
Estimate by rounding to the nearest integer.
B. 28.3 – 11.7
28.3
28
3 < 5, so round to 28.
–11.7
–12
7 > 5, so round to 12.
16
Course 2
Estimate
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Additional Example 1C: Estimating Sums and
Differences of Decimals
Estimate by rounding to the nearest integer.
C. 57.2 + (–23.72)
57.2
+ (–23.72)
57
+ (–24)
33
Course 2
2 < 5, so round to 57.
7 > 5, so round to –24.
Estimate
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Try This: Example 1A
Estimate by rounding to the nearest integer.
A. 6.7 + 4.9
6.8
+4.9
Course 2
7
8 ≥ 5, so round to 7.
+5
12
9 > 5, so round to 5.
Estimate
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Try This: Example 1B
Estimate by rounding to the nearest integer.
B. 19.2 – 13.6
19.2
19
–13.6
–14
5
Course 2
2 < 5, so round to 19.
6 > 5, so round to –14.
Estimate
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Try This: Example 1C
Estimate by rounding to the nearest integer.
C. 61.3 + (–18.84)
61.3
+ (–18.84)
61
+ (–19)
42
Course 2
3 < 5, so round to 61.
8 > 5, so round to –19.
Estimate
4-1 Estimate with Decimals
You can use compatible numbers when
estimating.
Compatible numbers are numbers that
replace the numbers in the problem and
are easier to use.
Course 2
4-1 Insert Lesson Title Here
Guidelines for Using Compatible Numbers
When multiplying. . .
round numbers to the
nearest nonzero integer
or to numbers that are
easy to multiply.
Course 2
When dividing. . .
round numbers so that
they divide without leaving
a remainder.
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Additional Example 2A: Estimating with Decimals
Use compatible numbers to estimate.
A. 45.99 · 2.31
45.99
 2.31
Course 2
2
Round to the nearest
multiple of 10.
3 < 5, so round to 2.
100
Estimate
50
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Additional Example 2B: Estimating with Decimals
Use compatible numbers to estimate.
B. 51.33 ÷ (–7.98)
51.33
49
51 is prime, so round to 49.
–7.98
–7
–7 divides into 49
without a remainder.
49 ÷ –7 = –7
Course 2
Estimate
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Try This: Example 2A
Use compatible numbers to estimate.
A. 39.62 · 4.99
39.62
 4.99
Course 2
5
Round to the nearest
multiple of 10.
9 > 5, so round to 5.
200
Estimate
40
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Try This: Example 2B
Use compatible numbers to estimate.
B. 19.42 ÷ (–4.88)
19.42
20
19 is prime, so round to 20.
–4.88
–5
–5 divides into 20
without a remainder.
20 ÷ –5 = –4
Course 2
Estimate
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Additional Example 3: Application
Cara spent $58.80 on 4.8 pounds of lobster and
calculated that she spent about $12 per pound of
lobster. Use estimation to check whether her
calculation is reasonable.
$58.80
$60
Round to the nearest
multiple of 10.
4.85
5
8 > 5, so round to 5.
60 ÷ 5 = 12
Estimate
The estimate is the same as Cara’s calculation.
The lobster cost about $12 per pound.
Course 2
4-1 Estimate
Insert Lesson
Title Here
with Decimals
Try This: Example 3
Clem spent $18.43 on 11.7 pounds of
apples. Is it reasonable to say that Clem
spent about $2 per pound on apples?
18.43
11.7
20 ÷ 10 = 2
$20
10
Round to the nearest
multiple of 10.
10 divides evenly into 20
without a remainder.
Estimate
The estimate is the same as Clem’s calculation.
The apples cost about $2 per pound.
Course 2
4-1 Estimate
Insert Lesson
with Decimals
Title Here
Lesson Quiz: Part 1
Estimate by rounding to nearest integer.
1. 68.4 + 29.5 98
2. 7.24 + (–10.5) –4
Use compatible numbers to estimate.
Possible answers:
3. 48.27  4.67 250
4. 54.37  5.67 9
Course 2