Multiplying Decimals and Circumference of a Circle Section 5.3 Multiplying Decimals and Circumference of a Circle

Multiplying Decimals Steps Count the number of places after the decimal for each number (a, b), and add together (a + b = c) Drop decimal Multiply the two numbers together. Put decimal at the end of the number and move the decimal to the left C places.

Example Simplify (0.15)( 1.25)

Example Simplify 61.7 x 58.12

10’s Multiplying Decimals by Powers of 10 Such as 10, 100, 1,000, 10,000 Move the decimal point to the right the same number of places as there are zeros in the power of 10 10 :move the decimal to the right 1 place 100 : move the decimal to the right 2 places 1,000 : move the decimal to the right 3 places 10,000 : move the decimal to the right 4 places.

Example Simplify 63.76 * 100

Example Simplify -123.56897 * 1000

10’s Multiplying Decimals by Powers of 10 Such as 0.1, 0.01, 0.001, 0.0001, etc Move the decimal point to the left the same number of places as there are decimal places in the power of 10 0.1 : move the decimal to the left 1 places 0.01 : move the decimal to the left 2 places 0.001 : move the decimal to the left 3 places. 0.0001 : move the decimal to the left 4 places.

Example Simplify 7.125 * 0.1

Example Simplify 459 * 0.01

Circumference C = 2πr C = πd π = 22/7 or π = 3.14

Example Find the circumference. Let π = 22/7

Example Find the circumference. Let π = 3.14

Example The London Eye, built for the millennium celebrations in London, resembles a gigantic Ferris wheel with a diameter of 135 meters. If Adam Hawn rides the Eye for one revolution, find how far he travels. Given an exact answer and an approximation using 3.14 for pi.