math CHAPTER 11

CHAPTER 11 PERCENTAGES

·      11.1 à some percentages are easy to find because they are simple fractions. they are example of these on the first page of this unit, you can use the easy ones to work out more complicated percentages. You can often do this quite easily. You do not always need a calculator.

·      Example:

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

100%=4600

58%= 50%+10%-2%--> these all the easy percentages to find.

50%=2300à 50%=1/2

10%=460à1/10 is easy. Just divide by 10

1%46àdivide 10% by 10 to find 1

58%= 2300+460-(2x46)= 2668 à do this sum in your head / on your paper.

Otherà you could have found 50%+5%+3%. Is that easier? J

Ø 90% of 320=?--> 320-3.2= 316.8

Ø show that 20% of 45 is the same as 45% of 20.

  So,   and     the result both of them are same.

·        11.2 à 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, 273 students took an exam and 147 passed. Which school did better? It’s hard to say because each school had a different number of students. The worked example shows how to use percentages to help to answer question like this.

·      Example:

Ø    In school A, 85 students took a mathematics exam and 59 passed.in school B 237 students took a mathematics exam and 147 passed. Which school had better pass rate?

59 out of 85 = 59 ÷ 85 = 69%  à  59 ÷ 85 = 0,694... =69% to the nearset whole number.

147 out of 237 = 147 ÷ 237 = 62%  à 147 ÷ 237 = 0,620.. =62%  to the nearset whole number.

The pass rate in school B is better by seven percentages points. à the difference between 62% and 69% is given on ‘percentages points.’

·       11.3 you can use percentages to describe a change in a quality. It could be an increase or a decrease. a percentages change is always calculated as apercentages f the initial value. The initial value is 100%. It is impothant to choose the correct value to be 100%