41 Understanding Percentages
Now that we understand fractions and ratios, lets take a look at percentages.
A percentage is a ratio that can be expressed as a fraction of 100. “Per” “cent” means “part of 100” (cent is Latin for 100). If we need to know the percent of a number, we simply divide by 100.
The symbol used for percent is %.
What is 40% of 80? Ways to achieve:
- 0.40 × 80 = 32
- 40 × 80 ÷ 100 = 32
Percent as a fraction:
- 10% is equal to [latex]\tfrac{1}{10}[/latex] fraction
- 20% is equivalent to [latex]\tfrac{1}{5}[/latex] fraction
- 25% is equivalent to [latex]\tfrac{1}{4}[/latex] fraction
- 50% is equivalent to [latex]\tfrac{1}{2}[/latex] fraction
- 75% is equivalent to [latex]\tfrac{3}{4}[/latex] fraction
- 90% is equivalent to [latex]\tfrac{9}{10}[/latex] fraction
Example
A recipe for pancakes uses 3 cups of flour and 2 cups of milk.
So the ratio of flour to milk is [latex]3:2[/latex].
To make pancakes for a lot of people, we might need 4 times the quantity, so we multiply the numbers by 4:
[latex]3\times4:2\times4=12:8[/latex]
In other words, 12 cups of flour and 8 cups of milk.
The ratio is still the same, so the pancakes should be just as yummy.
