Percentages
- 1. Percentages
- 2. Learning objectives Describe the meaning of percentage Identify the amount in a percent problem Identify the base in a percent problem Identify the percent in a percent problem Find the unknown quantity (amount, base or percent) in a percent problem
- 3. What is a percentage A percentage is the top part of a fraction whose bottom part is 100. Percentages are useful because they make it very easy to compare things.
- 4. What is a percentage: examples 50% means a half 25% means a quarter 50 100 ® 25 100 ®
- 5. What is a percentage: examples Percentages are useful because they make it very easy to compare things: I got different marks in two exams: I got 24/30 in the first exam and 36/60 in the second one. How can I compare these marks? I can change in some way the maximum mark to 100 for both the exams: Now I can compare the marks. 24 30 = 80 100 and 36 60 = 60 100
- 6. The three parts of a percent problem The base is the whole in a percent problem The amount is a part of the whole The percent (or rate) is the ratio of the amount to the base, written as a percent
- 7. The three parts of a percent problem Calculate the 20% of 800: So 160 is the 20% of 800 In this example 160 is the amount, 800 is the base and 20 is the percent. 800 100 ×20 =160
- 8. Exercise Identify base, amount and percent in the following examples: 21 is the 70% of 30 36 is the 60% of 60 Amount Base Percent
- 9. How to calculate percent = amount base 100 base = amount percent 100 amount = percent × base 100
- 10. Examples Calculate the 20% of 300 The percent is 20%, the amount is 30, calculate the base: 300 100 20 = 60 base = 30 20 100 =150
- 11. Examples The amount is 15, the base is 60, calculate the percent percent = 15 60 100 = 25%
- 12. Exercise Complete the table Amount Base Percent 30 90 80 15 25 40