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Multiplying Decimals and Circumference of a Circle

Section 5.3. Multiplying Decimals and Circumference of a Circle. 21. 7. 3. x. 1000. 10. 100. Multiplying Decimals. Multiplying decimals is similar to multiplying whole numbers. The difference is that we place a decimal point in the product. 0.7 x 0.03 =. =. = 0.021.

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Multiplying Decimals and Circumference of a Circle

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  1. Section 5.3 Multiplying Decimals and Circumference of a Circle

  2. 21 7 3 x 1000 10 100 Multiplying Decimals Multiplying decimals is similar to multiplying whole numbers. The difference is that we place a decimal point in the product. 0.7 x 0.03 = = = 0.021 1 decimal place 2 decimal places 3 decimal places Martin-Gay, Prealgebra, 5ed

  3. Multiplying Decimals Step 1. Multiply the decimals as though they were whole numbers. Step 2. The decimal point in the product is placed so the number of decimal places in the product is equal to the sumof the number of decimal places in the factors. Martin-Gay, Prealgebra, 5ed

  4. Estimating when Multiplying Decimals Multiply 32.3 x 1.9. Exact Estimate rounds to rounds to This is a reasonable answer. Martin-Gay, Prealgebra, 5ed

  5. Multiplying Decimals by Powers of 10 There are some patterns that occur when we multiply a number by a power of ten, such as 10, 100, 1000, 10,000, and so on. Martin-Gay, Prealgebra, 5ed

  6. Multiplying Decimals by Powers of 10 76.543 x 10 = 765.43 76.543 x 100 = 7654.3 76.543 x 100,000 = 7,654,300 Decimal point moved 1 place to the right. 1 zero Decimal point moved 2 places to the right. 2 zeros Decimal point moved 5 places to the right. 5 zeros The decimal point is moved the same number of places as there are zeros in the power of 10. Martin-Gay, Prealgebra, 5ed

  7. Multiplying by Powers of 10 such as 10, 100, 1000 or 10,000, . . . Move the decimal point to theright thesame number of places as there arezerosin the power of 10. Multiply: 3.4305 x 100 Since there are two zeros in 100, move the decimal place two places to the right. 3.4305 x 100 = 3.4305 = 343.05 Martin-Gay, Prealgebra, 5ed

  8. Multiplying by Powers of 10 such as 0.1, 0.01, 0.001, 0.0001, . . . Move the decimal point to theleft thesame number of places as there aredecimal placesin the power of 10. Multiply: 8.57 x 0.01 Since there are two decimal places in 0.01, move the decimal place two places to the left. 8.57 x 0.01 = 008.57 = 0.0857 Notice that zeros had to be inserted.

  9. Finding the Circumference of a Circle The distance around a polygon is called itsperimeter. The distance around a circle is called thecircumference. This distance depends on theradiusor thediameter of the circle. Martin-Gay, Prealgebra, 5ed

  10. Circumference of a Circle r d Circumference= 2·p·radius or Circumference =p·diameter C= 2prorC=pd Martin-Gay, Prealgebra, 5ed

  11. 22 7 p The symbolpis the Greek letter pi, pronounced “pie.” It is a constant between 3 and 4. A decimal approximation forpis 3.14. A fraction approximation forpis. Martin-Gay, Prealgebra, 5ed

  12. 4 inches Find the circumference of a circle whose radius is 4 inches. C= 2pr= 2p·4= 8pinches 8p inches is the exact circumference of this circle. If we replace  with the approximation 3.14, C= 8  8(3.14) = 25.12 inches. 25.12 inches is the approximate circumference of the circle.

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