Math- Unit 11 Theory (Percentages)

Percentages are used, instead of actual numbers, in articles in newspapers ang magazines, on television or on internet. Percentages are easier to interpret than the actual numbers if you want to: - describe one number as a fraction of another -describe an increase or decrease -compare two different fractions or two different increases or decreases Calculating percentages: Parcentage means 'out of 100', so a percentage is just a fraction with 100 as the denominator. You need to be able to write percentages as fractions. If the percentage is a simple fraction, you should be able to work it mentally. For other percentages, you could use a calculator. Percentage increases and decreases: Percentages are often used to describe increase and decrease. Example: The population of the town decreased by 13% I receive a 7% pay rise The price was reduced by 30% Production was rose by 150% You can find the result of an increase or decrease in two steps. 1.First, calculate the increase or decrease. 2.Then add it to or subtract it from the original amount. Finding percentages: There are times when you need to write one number as a percentage of another. Here are some exmaples: -writing a price increase as percentage -finding the percentage of people who are unemployed -estimating the percentage change in population To write one number as a percentage of another, write the numbers in the form of a fraction and then change the fraction to a percentage. If the numbers are simple, you can do this mentally. For more complicated numbers,use a calculator. Using percentages The price of a scarf increases from $20 to $25 The price of a coat increases from $100 to $105 The prices have increased by the same amount but they have not increased by the same percentage. Percentages are a better way than amounts to compare changes of this sort.