concepts and questions of Percentages.ppt

concepts and questions of Percentages.ppt

• 1.
  How to dealwith percentage problems
• 2.
  How to changepercentages, into fractions and decimals A percentage is a special fraction. The % says, “per hundred.” For example, 47%, is simply another way of writing the fraction 47/100
• 3.
  You can almostsee the 100 in the percentage sign The 1 The noughts Percentage Fraction 7% 7/100 19% 19/100 83% 83/100 Etc.
• 4.
  24% = 24/10012/50 6/25 So to write a percentage as a fraction, you simply put it over 100 like this: 24% = 24/100 Yes, but remember to try to write the fraction in its simplest terms
• 5.
  Copy and completethis chart Percentage Fraction Percentage Fraction 1. 23% 23/100 7. 80% 2. 24% 8. 84% 3. 55% 9. 12% 4. 20% 1/5 10. 48% 5. 17% 11. 71% 6. 78% 12. 36%
• 6.
  To change afraction into a decimal, you divide the bottom number (the denominator) into the top number (numerator). For example, to change ¾ into a decimal, you would divide the 3 by the 4. ¾ 3 ÷ 4 = 0.75 Remember that a percentage is a fraction always has 100 as its denominator
• 7.
  So, to changea percentage into a decimal, you always divide by 100 For example, 35% as a fraction is 35/100 so to change this into a decimal, you divide 35 by 100 35% 0.35 ÷ 100
• 8.
  To change decimalinto a percentage Decimal Percentage To change a decimal into a percentage, you X by 100 0.23 23% X 100
• 9.
  You Should Know Aa percentage is a special fraction. 23% = 23/100 Percentage to a decimal ÷ 100 Decimal to a percentag e X 100
• 10.
  Copy and completethis chart Percentage Decimal Decimal Percentage 1. 27% 7. 0.87 2. 2% 8. 0.08 3. 55% 9. 0.42 4. 5% 10. 0.04 5. 17% 11. 0.71 6. 98% 12. 0.07
• 11.
  Finding one quantityas a percentage of another quantity Jill obtained a score of 23 out of 32 in a science test. She wants to know what this will be as a percentage? To do this, you • Write the result as a fraction 23/32 • 4. 72% • Change the fraction into a decimal (23 ÷ 32 = 0.71875) • Change the decimal into a % (0.71875 X 100 = 71.9%)
• 12.
  There are lotsof similar problems and all of these can be tackled in the same way 1. Write the quantities as a fraction 23/32 2. Change the fraction into a decimal (23 ÷ 32 = 0.71875). It’s probably a good idea to round off to 2 decimal places. 3. Change the decimal into a % (0.72 X 100 =72%) 4. So, 23 is 72% of 32 The total quantity The quantity that you want as a %
• 13.
  Car Par Survey ColourFrequency Green 2 Silver 4 Black 5 What percentage of the cars are green? Total is 11 Want 2/11 as a percentage Change 2/11 into a decimal = 0.1818 (round off to 2 d,p. Change 0.18 into a % (0.18 X 100 = 18%) Answer 18%
• 14.
  Try these: 1 Workout your percentage if you got 12 out of 25 2 Work out your percentage if you got 15 out of 25 3 Work out your percentage if you got 17 out of 20 4 Work out your percentage if you got 19 out of 24 5 Work out your percentage if you got 17 out of 31 6 A player scores 3 times out of 6 shots.What is their score percentage 7 A player scores 4 times out of 10 shots. What is their score percentage 8 A player scores 44 times out of 69 shots. What is their score percentage 9 Work out 12.5 out of 26 as a percentage 10 Calculate the score percentage if out of 15 shots 12 are successful
• 15.
  The ‘percentage of’problem What is 12% 0f 34? What is 13% of 56? What is 78% of 57?
• 16.
  To answer thesequestions First: Change the percentage into a decimal Second: Change the word ‘of’ into a X sign Third: Workout Example: What is 23% of 45 23% = 0.23 and ‘of’ X 0.23 X 45 = 10.35
• 17.
  Finding Percentages ofDifferent Numbers Problem: In a survey of 120 pupils it was found that 20% had personal stereos. How many pupils had personal stereos? Change the percentage to a decimal, then multiply by the number of children. 20% = 0.20 0.20 times 120 = 24
• 18.
  1. 25% of32 2. 75% of 36 3. 80% of 35 4. 10% of 142 5. 20% of 60 6. 35% of 70 7. 6% of 220 8. 15% of 150 9. 12% of 20 10. 27% of 30 Try these