Course 2 Chapter 1 Section 1

Using Estimation Strategies

Reviewing Skills You Need:

Round the Place to the underlined Digit

3,528

100:

Estimate

3,500

24,106

10:

Estimate

24,110

54

10:

Estimate

50

131,295

10,000:

Estimate

130,000

82,729

1,000:

Estimate

83,000

Objective 1: Estimating by Rounding

Example 1: Estimating a Sum or Difference

At the zoo, you see a Columbian 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 cm + 78.96 cm ≈

58.3 cm + 79.0 cm Round to the nearest tenth

137.3 cm Add

Objective 1: Estimating by Rounding

Example 2: Estimating a ProductA 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 ft. × 5.75 ft ≈

9 ft. × 6 ft. Round to the nearest whole foot

54 square feet Multiply

Objective 2: Estimating by Front-End Estimation and

Compatible Numbers

Example 3: Estimating with Front-End Estimation

At a snack shop, you order a taco that costs $3.79, a juice that costs $.89, and a yogurt that costs $1.39. Estimate the total cost of your order.

Step 1: Add the front end digits

$3.79$0.89$1.39+$4

Step 2: Estimate the total amount of cents to the

nearest dollar.

$3.79$0.89$1.39+

About $2

Step 3: Add the dollars and Estimated cents

+$4 $2 = $6

Total cost is about $6

Compatible Numbers:(Friendly Numbers)Compatible Numbers are numbers that are easy to compute mentally. Compatible Numbers are particularly useful to solve quotients.

Example 4: Estimating Using Compatible Numbers

Suppose you have saved $61.80. About how many CD’s can you buy if each costs $15.95?

$61.80 ÷ $15.95 ≈

$60 ÷ $15 ≈ 4

About 4 CD’s

Questions?

Assignment: Practice 1-1 Worksheet