6-2 Estimating with Percents Warm Up Warm Up California Standards California Standards Lesson Presentation Lesson PresentationPreview

6-2 Estimating with Percents Warm Up Write each percent as a fraction %2. 75% 3. 20%4. 60%

6-2 Estimating with Percents NS1.3 Convert fractions to decimals and percents and use these representations in estimations, computations, and applications. California Standards

6-2 Estimating with Percents Vocabulary estimate compatible numbers

6-2 Estimating with Percents Some problems require only an estimate. Estimates involving percents and fractions can be found by using compatible numbers, numbers that go well together because they have common factors and 24 are compatible numbers because 12 is a common factor of 12 and and 24 are not compatible numbers.

6-2 Estimating with Percents When estimating with percents, it helps to know some benchmarks. Benchmarks are common numbers that serve as points of reference. Some common benchmarks for percents are shown in the table.

6-2 Estimating with Percents Estimate. 21% of 66 Additional Example 1A: Estimating with Percents 21% ≈ 20%Use a benchmark close to 21%. ≈ 1 5 Write 20% as a fraction. 66 ≈ 65 Use compatible numbers. 1 5  65 = 13 Use mental math: 65 ÷ 5. So 21% of 66 is about 13.

6-2 Estimating with Percents Estimate. 36% of 120 Additional Example 1B: Estimating with Percents 36%  35% Round.  30% + 5%Break down the percent into smaller parts.  3  10% + 5% 35%  120 = (3  10% + 5%)  120 Set up an equation.

6-2 Estimating with Percents Additional Example 1B Continued = % of 120 is 12, so 5% of 120 is 6. = 42 So 36% of 120 is about 42. = 3  10%  %  120 Use the Distributive Property.

6-2 Estimating with Percents Estimate. 29% of 86 Check It Out! Example 1A 29% ≈ 30%Use a benchmark close to 29%. ≈ 3 10 Write 30% as a fraction. 86 ≈ 90Use compatible numbers, 90 and  90 = 27 Use mental math: 90 ÷ 10. So 29% of 86 is about 27.

6-2 Estimating with Percents Estimate. 44% of %  45%Round.  40% + 5%Break down the percent into smaller parts.  4  10% + 5% 45%  130 = (4  10% + 5%)  130 Set up an equation. Check It Out! Example 1B

6-2 Estimating with Percents = % of 130 is 13, so 5% of 130 is 6.5. = 58.5 So, 44% of 130 is about = 4  10%  %  130 Set up an equation. Check It Out! Example 1B Continued

6-2 Estimating with Percents Maria took her mother out to lunch for her birthday. The check for lunch was $ If Maria wants to leave about a 15% tip, about how much should she pay? Additional Example 2: Problem Solving Application

6-2 Estimating with Percents Additional Example 2 Continued 1 Understand the Problem The answer is the total amount Maria should pay for their lunch. List the important information: The total cost of lunch was $ Maria wants to leave a 15% tip.

6-2 Estimating with Percents 2 Make a Plan Use estimation and mental math to find the tip. Then add the tip to the check amount to find the total amount Maria should pay. Additional Example 2 Continued

6-2 Estimating with Percents Solve 3 Additional Example 2 Continued First round $20.15 to $20. 15% = 10% + 5% 10% of $20 = $2.00 5% of $20 = 10%  2 = $ % = 10% + 5% = $ $1.00 = $3.00 $ $3.00 = $23.15 Maria should pay about $23.15.

6-2 Estimating with Percents Look Back4 Additional Example 2 Continued Use a calculator to determine whether $3.00 is a reasonable estimate of a 15% tip  0.15  3.02, so $3.00 is a reasonable estimate.

6-2 Estimating with Percents Fred and Claudia went out to lunch. The total cost of their food was $ If they want to leave a 15% tip, about how much should they pay? Check It Out! Example 2

6-2 Estimating with Percents Check It Out! Example 2 Continued 1 Understand the Problem The answer is the total amount Fred and Claudia should pay for lunch. List the important information: The total cost of lunch was $ They want to leave a 15% tip.

6-2 Estimating with Percents 2 Make a Plan Check It Out! Example 2 Continued Use estimation and mental math to find the tip. Then add the tip to the check amount to find the total amount they should pay.

6-2 Estimating with Percents Solve 3 Check It Out! Example 2 Continued First round $24.85 to $25. 15% = 10% + 5% 10% of $25 = $2.50 5% of $25 = 10%  2 = $ % = 10% + 5% $ $3.75 = $28.60 They should pay about $ = $ $1.25 = $3.75

6-2 Estimating with Percents Look Back4 Check It Out! Example 2 Continued Use a calculator to determine whether $3.75 is a reasonable estimate of a 15% tip  0.15  3.73, so $3.75 is a reasonable estimate.

6-2 Estimating with Percents Additional Example 3: Printing Application A printing company has determined that approximately 6% of the books it prints have errors. Out of a printing run of 2050 books, the production manager estimates that 250 books have errors. Estimate to see if the manager’s number is reasonable. Explain. 6%  2050 ≈ 5%  2000Use compatible numbers. ≈ 0.05  2000Write 5% as a decimal. Multiply. ≈ 100 The manager’s number is not reasonable. Only about 100 books have errors. 250 is much greater than 100.

6-2 Estimating with Percents Check It Out! Example 3 A clothing company has determined that approximately 9% of the sheets it makes are irregular. Out of a shipment of 4073, the company manager estimates that 397 sheets are irregular. Estimate to see if the manager’s number is reasonable. Explain. 9%  4073 ≈ 10%  4000Use compatible numbers. ≈ 0.10  4000Write 10% as a decimal. Multiply. ≈ 400 Because 397 is close to 400, the manager’s number is reasonable.

6-2 Estimating with Percents Lesson Quiz: Part I Estimate % of % of Ian had dinner with some friends at a restaurant. The check for his dinner was $ If he wants to leave a 20% tip, what is the total amount Ian should pay? 4 90 Possible answer: $12.25 Possible answers:

6-2 Estimating with Percents Lesson Quiz: Part II 4. Approximately 8% of each batch of jeans produced at one factory is defective. Ms. Fleming said that in a batch of 400 jeans, about 35 jeans would be defective. Estimate to determine if her number is reasonable. Explain. Yes, because 8% of 400 is a little less than 10% of % of 400 is 40, and 35 is a little less than 40.