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Section 3A Uses and Abuses of Percentages

Section 3A Uses and Abuses of Percentages. Pages 133-147. fraction. decimal/ proportion. percentage. 3-A. per cent = “per 100” = “divided by 100”. 47% = 47/100 = .47 2% = 2/100 = .02 813% = 813/100 = 8.13. 3-A.

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Section 3A Uses and Abuses of Percentages

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  1. Section 3AUses and Abuses of Percentages Pages 133-147

  2. fraction decimal/ proportion percentage 3-A per cent = “per 100” = “divided by 100” 47% = 47/100 = .47 2% = 2/100 = .02 813% = 813/100 = 8.13

  3. 3-A To convert a percentage to a decimal simply divide by 100 , or move the decimal two places to the left 45% = 45/100 = .45 1.2% = 1.2/100 = .012 714% = 714/100 = 7.14 To convert a decimal to a percentage simply multiply by 100% (=1), or move the decimal two places to the right: .16 = .16 * 100% = 16% 2.3 = 2.3 * 100% = 230%

  4. 3-A To convert a percentage to a fraction simply divide by 100 (and reduce as necessary): 45% = 45/100 = 9/20 1.3% = 1.3/100 = 13/1000 525% = 525/100 = 21/4 To convert a fraction to a percentage simply divide to get a decimal and then move decimal two spaces to the right: 1/5 = .20 = .20 * 100% = 20% 5/4 = 1.25 = 1.25*100% = 125%

  5. 3-A 3 Ways of Using Percentages • As fractions – “Percent of” • To describe change over time • For comparison

  6. 3-A 1. Percent “of “ - (multiply) In 2004,9.7% of the citizens in Virginia lived in poverty. The population of Virginia was 7,495,827. How many people in Virginia were living in poverty? ‘9.7% × 7,459,827’ = .097 × 7,459,827 = 727,095.219 = 727,095 people

  7. 3-A More Practice Suppose A is 75 and B is 480. A is ____________ percent of B. B is ____________ percent of A. So, A is 15.625% of B. and B is 640% of A.

  8. 3-A More Practice 345 blooming tulips in a field of 398 tulips. The blooming tulips are __??___ percent of the field.

  9. 3-A 2. Percents are often used to describe how a quantity changes over time Given: original value and new value

  10. 3-A Absolute Change vs. Relative Change John’s salary grew from $20,000 in 2001 to $28,000 in 2003. absolute change=$28,000 – $20,000 = $8000 relative change =$8000/$20,000 = .40 = 40% John’s salary in 2003 was 40% more than his salary in 2001. [John’s salary in 2003 was 28,000/20,000 = 1.40 =140% ofhis salary in 2001.]

  11. 3-A Absolute Change vs. Relative Change A computer you bought three years ago for $1000 is today worth only $300. absolute change=$300 – $1000 = -$700 relative change =-$700/$1000 = -.70 = -70% The value of the computer today is 70% less than its value three years ago. [The computer’s value today is 300/1000 = .30 =30% ofthe value in 2003.]

  12. 3-A Percentage Of vs. More (or Less) Than(page 140) If the new value is P% more than the original value, then the new value is (100+P)%of the original value. If the new value is P% less than the original value, then the new value is (100-P)%of the original value.

  13. 3-A Absolute Change vs. Relative Change Today,my stock doubled in price from $1000 to $2000. absolute change =$2000 – $1000 = $1000 relative change =$1000/$1000 = 1 = 100% The value of stock today is 100% more than yesterday’s value. (Today’s price is 200% of yesterday’sprice.)

  14. 3-A Absolute Change vs. Relative Change How much would stock have to grow to in order to see a relative change of 200%? relative change = 200%= 2 = $2000/$1000 absolute change =$2000 =$3000– $1000 So my stock had to triple in value.

  15. 3-A Homework Pages 148-150 # 22, 30, 50, 52, 56 Express your answers in sentence form.

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