1. Chapter 8 Percentages

2. Learning Objectives Write a percentage as a fraction in its simplest form Change a percentage to a decimal Change a decimal to a percentage Change a fraction to a percentage Express one quantity as a fraction of another Find a percentage of a quantity Increase/decrease a quantity by a percentage Do standard form percentage problems Find percentage increase/decrease Do reverse percentage problems

3. Converting to a Percentage Simply multiply by 100 Examples Convert the following to percentages 1) 17 / 50 2) 5 / 9 3) 0.34

4. Converting from a Percentage Percentage to Decimal  Divide by 100 Examples 1) 34% 2) 17.5% Percentage to Fraction  Divide by 100 Example 1) 34% 2) 17%

5. Percentage Marks Example In a class test the following marks were obtained. Write each mark as a percentage. (a) Susan 34 out of 50 (b) Ben 17 out of 20 (c) John 21 out of 25 (d) Kate 48 out of 60

6. Expressing as a Percentage Put the 1 st quantity over the second quantity and multiply by 100 Examples 1)Express 40p as a percentage of £3 2)A paper has 48 pages, 6 of which are sports pages. What percentage is this?

7. Finding a Percentage of a Quantity Put the percentage over 100 and multiply Examples 1.Find 20% of £56 2.Pat invests £300 in a saving account and earns 6% interest per year. How much interest does he get in a year?

8. Percentage of a Quantity Put the percentage over 100 and multiply Examples 1)A shirt is normally priced at £24. It is reduced by 15% in a sale. How much is the shirt now? 2)A car was valued at £21000. It depreciated by 24% in the 1 st year. What was it worth at the end of the year?

9. Harder Percentage Problems 1. Calculate 4×10 6 as a percentage of 2×10 8. 2. 1.2×10 10 steel cans were used in 1992. 1.4×10 9 of these were recycled. Calculate the percentage of cans not recycled. 3. Calculate 30% of 8×10 9

10. Percentage Increase/ Decrease Percentage increase or decrease = increase or decrease ÷ original × 100 Examples 1)A sample of soil is dried in an oven. Its mass reduced from 65g to 45g. What is its percentage decrease? 2)A shop buys pens for 15p and sells them for 21p. What is the percentage profit?

11. Reverse Percentage Problems Examples (1)A shop sells DVDS with 20% discount for a special promotion. If a DVD costs £10 in the sale, how much is it normally? (2)Tara gets a 5% wage rise. Her new wage is £126. What was her wage before the increase?