A percentage is a number expressed as a fraction of 100. It is denoted using the percent sign, %.
By the end of this section you should be able to: ● fi nd a percentage of a number ● express one number as a percentage of another
● use percentages to solve problems in context
When the number is complete or whole then you have 100%. If there are 30 students in your class and everyone is in school, then we have 100% attendance. If you score 64% on a test, then you have scored 64 out of 100.
Expressing a number as a percentage of another number To express one number as a percentage of another, for example €30 out of €400, follow these steps:
1
2 3
Write the numbers as a fraction of each other €30 out of €400 = 30 30
Multiply by 100 Add the % symbol
___ 400
___ 400 × 100 = 7·5
= 7·5% So €30 is 7 · 5% of €400
Finding a percentage of a number To determine the percentage of a number, for example 15% of 200, follow these steps:
1 2
Convert the percentage to a fraction Multiply the fraction by the number
15% = 15 15
___ 100 × 200
___ 100 × 200 = 3 000
15
___ 100 = 30
So 15% of 200 is 30
Finding a number, when given a percentage of it To determine the entire number when given a percentage of it, for example 12% of a number is 72, follow these steps:
1 2 Find 1% of the number by dividing both sides by the given percentage Multiply both sides by 100 to fi nd the entire number