Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. 4.4 Multiplying Decimals and Circumference of a Circle

Martin-Gay, Basic Mathematics, 4e 22 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Multiplying Decimals Multiplying decimals is similar to whole numbers. The only difference is that we place a decimal point in the product. Multiplying Decimals Step 1: Multiply the decimals as though they are whole numbers. Step 2: The decimal point in the product is placed so that the number of decimal places in the product is equal to the sum of the number of decimal place in the factors.

Martin-Gay, Basic Mathematics, 4e 33 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Multiplying Decimals StepExample Step 1: Multiply the decimals as though they are whole numbers. Multiply: Step 2: The decimal point in the product is placed so that number of decimal places in the product is equal to the sum of the number of decimal places in the factors. Total of 2 decimal places. Decimal placed at two decimal places.

Martin-Gay, Basic Mathematics, 4e 44 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Example Multiply: 15.9 × decimal place 2 decimal places Insert the decimal point in the product so that there are 3 decimal places (1 + 2 = 3).

Martin-Gay, Basic Mathematics, 4e 55 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Example Multiply: × decimal places 1 decimal place Insert the decimal point in the product so that there are 4 decimal places.

Martin-Gay, Basic Mathematics, 4ed 66 1.Multiply 45.9 X Multiply X 0.6 Practice Problems Multiplying Decimals P decimal place 2 decimal places 1+2=3 decimal places 3 decimal places 1 decimal place 3+1=4 decimal places

Martin-Gay, Basic Mathematics, 4ed 77 3.Multiply X 48 Practice Problems Multiplying Decimals P decimal place 0 decimal places 4+0=4 decimal places

Martin-Gay, Basic Mathematics, 4e 88 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Estimating when Multiplying Decimals We can estimate when multiplying decimals to check for reasonableness. Example: ExactEstimate Since is close to our estimate of 20, it is a reasonable answer.

Martin-Gay, Basic Mathematics, 4ed 99 Estimating When Multiplying Decimals Practice Problem 4 SOLUTION Multiply: Exact Estimate Since is close to our estimate of 90, it is a reasonable answer. P 276 Round to the ones

Martin-Gay, Basic Mathematics, 4e 10 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Multiplying by Powers of 10 TypeExample Multiplying Decimals by Powers of 10 such as 10, 100, : Move the decimal point to the right the same number of places as there are zeros in the power of 10. Multiplying Decimals by Powers of 10 such as.1,.01, : Move the decimal point to the left the same number of places as there are decimal places in the power of 10.

Martin-Gay, Basic Mathematics, 4e 11 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Example Multiply. a.58.1 × 0.01 b.85,624 × 0.1 c ×100 = Move the decimal point 2 places to the left = Move the decimal point 1 place to the left. = Move the decimal point 2 places to the right.

Martin-Gay, Basic Mathematics, 4e 12 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. ProblemsAnswers P 277 Practice Problems Multiplying by Powers of 10

Martin-Gay, Basic Mathematics, 4e 13 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. ProblemsAnswers P 277 Practice Problems Multiplying by Powers of 10

Martin-Gay, Basic Mathematics, 4e 14 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Finding the Circumference of a Circle DefinitionExample Circumference: The distance around a circle. diameter radius The two common approximations for

Martin-Gay, Basic Mathematics, 4e 15 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Example Find the circumference of the following circle. Circumference = 9.1 yards

Martin-Gay, Basic Mathematics, 4e 16 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Solving Problems by Multiplying Decimals Jose Severos, an electrician for Central Power and Light, worked 40 hours last week. Calculate his pay before taxes for last week if his hourly wage is $ Jose Severos’ pay before taxes for last week is $

Martin-Gay, Basic Mathematics, 4e 17 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. Finding the Circumference of a Circle Practice Problem 12 SOLUTION Find the circumference of a circle whose radius is 11 meters. Then use the approximations 3.14 for π to approximate this circumference. 11 meters P 278

Martin-Gay, Basic Mathematics, 4e 18 Copyright © 2011 Pearson Education, Inc. Publishing as Prentice Hall. DONE