Chapter 11

Chapter 11: Percentages

11.1 Using mental methods:

In this chapter you will be learning more about percentages, some percentages are really easy to find because they are simple fractions. While others are difficult because the fractions are really hard to find.

Worked Example 11.1: These percentages are all easy to find

There are 4600 people in a stadium. 58% are males. How many is that?

100% = 4600                   

58% = 50% + 10% - 2%

50% = 2300

10% = 460

1% = 46

Question (Small Test):

19% of 256 = 48.64

Use this fact to find the question above:

      

        A.     19% of 128 B. 9.5% of 256 C. 19% of 512 D. 9.5 of 512

11.2 Comparing different quantities

You will often need to compare groups that are different sizes. Suppose that, in one school, 85 students took an exam and 59 passed. In another school, 237 students took an exam and 147 passed. Which school did better? It is hard to say because each school had a different number of students.

Worked Example 11.2: Which school had a better pass rate?

59 out of 85 = 59 ÷ 85 = 69%

147 out of 237 = 147 ÷ 237 = 62%

The pass rate in school B is better by seven percentage points