Quick Review

Round to the place value of the underlined digit:

1. 3, 528

2. 131,295

3. 229,000

4. 995

Answers:

1. 3,500

2. 130,000

3. 200,000

4. 1,000

Using Estimation Strategies

Section 1-1 (pages 5-9)

Estimate or Exact?

Suppose you are writing a news article. Your notes contain some data that may be estimates. For each situation, decide whether you have an estimate or an exact value. Explain your decision.

a) The population of Florida is 16,000,000.

b) Florida has 25 representatives in the U.S. House of Representatives.

Other examples??

Estimate

Exact Value

Things to Remember…

Estimate a number before you calculate it

Use the symbol which means “approximately equal to”

Estimating a Sum or Difference

At the zoo, you see a Colombian black spider monkey. The length of its body is 58.31 cm. The Length of its tail is 78.96 cm. To the nearest tenth of a centimeter, estimate the total length of the monkey’s body and tail.

58.31 + 78.96 58.3 + 79.0 Round to nearest tenth

Add 137.3 cm

Estimating a Product

A rectangular kitchen is 8.5 ft long and 5.75 ft wide. Use rounding to estimate the area of the kitchen in square feet.

8.5 9

5.75 6

Round each factor to the nearest whole number

9 * 6 = 54 ft2 Multiply

Extra Practice

Estimate. Round to the nearest whole number before you add or subtract

1) 10.13 + 1.46

2) 14.17 - 10.92

3) 11.53 + 7.23

4) 9.35 - 0.81

11

319

8

Extra Practice

Estimate. Round to the nearest whole number before you multiply.

1) 4.9 x 12.2

2) 6.07 x 3.29

3) 7.65 x 5.33

4) 25.123 x 4.79

601840

125

Estimating by Front-End Estimation

Useful for finding sums or differences. Two Steps:

1) Add (Subtract) the front numbers2) Estimate the sum of the lesser numbers and adjust the estimate

Estimating by Front-End Estimation

Suppose you went food shopping with your parents this weekend and bought Lucky Charms for $3.21, a frozen pizza for $4.79, Pepsi for $1.99, and a pack of gum for $1.15. Estimate the total cost of your purchases.

Step 1: Add the front-end

digits

$3.21

$4.79

$1.99

+$1.15

$9

Step 2: Estimate the total amount of cents to the nearest dollar.

$3.21

$4.79

$1.99

+$1.15

$2

About $1

About $1

The total cost is about $11.

Extra Practice A group of runners run a relay race in which each

runner decides how long they run for. Their distances were 3.9 miles, 2.1 miles, 1.7 miles, 1.2 miles, and 3.3 miles. Estimate the total distance of the race.

Step 1: Add the front-end

digits

3.9

2.1

1.7

1.2

+ 3.3

10

Step 2: Estimate the total amount of tenths of a mile to the nearest mile.

3.9

2.1

1.7

1.2

+ 3.3

2

About 1

About 1

The total distance is about 12 miles.

Extra Practice

Use Front-End Estimation to estimate each sum.

1) 5.43 + 2.67

2) 8.09 + 11.24

3) 7.18 + 5.89

4) 3.62 + 2.31

8

1913

6

What is a compatible number?

Numbers that are easy to compute mentally. You can use compatible numbers to estimate.

Change the numbers of the problem to make the calculation easier.

Useful for finding quotients.

Using Compatible Numbers It took 75.75 pounds of shredded cheese to make

the world’s largest burrito. Use compatible numbers to estimate how many 10 pound boxes of shredded cheese the cooks needed.

75.75

10Set up the Quotient

80

10

Choose compatible numbers such as 10 and 80.

Extra Practice

Use compatible numbers to estimate each quotient.

1) 76.5 ÷ 8.8

2) 19.45 ÷ 4.92

3) 103.6 ÷ 9.72

4) 32.2 ÷ 7.56

9

4

10

4