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Understanding Percentages: Converting Decimals and Fractions

This unit focuses on the concept of percentages and how to convert decimals and fractions into percent forms. It explains that "percent" means "per hundred" and illustrates how to represent various decimals as percentages by moving the decimal point two places to the right and adding a percent sign. Additionally, it covers methods for converting fractions to percentages, including adjusting denominators and multiplying by 100%. The unit concludes with practical examples and homework to reinforce learning.

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Understanding Percentages: Converting Decimals and Fractions

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  1. Unit 2 Percent

  2. Unit 2.1 Writing Decimals and Fractions as Percents

  3. What is percent? • It means Per – 100 (like 100 cents in a dollar) • When we say percent, we mean, how many equal parts of 100. • For example, “One percent” (written 1%) means 1 of 100 equal parts. (1/100) • “Fifty percent” (written 50%) means 50 out of 100. (50/100)

  4. What decimal is 1/100? So 1/100 is the same as 0.01 is the same as 1% What decimal is 50/100? So 50/100 is the same as 0.50 is the same as 50%

  5. Writing a decimal as a percent • To write a decimal as a percent, move the decimal point two places to the right and attach a percent sign (%). = 75% 0.75 .

  6. Examples • Write the following decimals as percents: • .35 • .42 • .58 35% 42% 58%

  7. More Examples • Try writing these decimals as percents: • .011 • .3467 • 2.6 • 0.008 1.1% 34.67% 260% .8%

  8. Writing a fraction as a percent • There are multiple ways to write a fraction as a percent. • Method 1: Convert the denominator of the fraction to 100, then the percent is the numerator. • Method 2: Multiply the fraction by 100%, then simplify. • Method 3: Change the fraction to a decimal, and then write it as a percent.

  9. Method 1: Convert the denominator of the fraction to 100, then the percent is the numerator. 40 100 8 20 5 5 = = 40%

  10. Method 2: Multiply the fraction by 100%, then simplify. 4 5 4 5 400% 5 = = =  100% 80% 3 8 = 37.5%

  11. Method 3: Change the fraction a decimal, and then write it as a percent. 1 2 = 0.5 = 50%

  12. Examples • Write the following fractions as percents. • 7/20 • 11/50 • 22/25 • 2/5 • 5/8 35% 22% 88% 40% 62.5%

  13. Writing a percent as a decimal. • To write a percent as a decimal, move the decimal point two places to the left and drop the percent sign (%). .75 . 75% =

  14. Examples • Change the following percents to decimals: • 35% • 50% • 325% • 37½% 0.35 0.5 3.25 0.375

  15. More Examples • Try writing these percents as decimals. • ½% • ¾% • ¼% 0.5% = .005 0.75% = .0075 0.25% = .0025

  16. Homework 1 • Find a newspaper article that mentions at least three different percentages. • Bring the article to class. • Hi-light the percentages. • Write in complete sentences what these percents are used for. • Change the percentages to decimals. • Change the percentages to fractions.

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