IT

CHAPTER 11: PERCENTAGES

11.1: Using Mental Methods

Ø  EXPLANATION:

·         Some percentages are easy to findà For Simple Fractions.

·         If you know 10%, you can find any multiple of 10%.

·         You can often do this quite easily. (Don’t always need a calculator)

Ø  EXAMPLE:

There are 4400 people in a stadium. 60% are males. How many is that?

ü  60% = 50% + 10%

ü  50% of 4400 = 2200

ü  10% of 4400 = 440

è 60% = 2200 + 440 = 2640

Work out:

ü  49% of 2300

ü  49% = 50% - 1%

ü  50% of 2300 = 1150

ü  1% of 2300 = 23

ü  49% = 1150 – 23 = 1127

ü  110% of 36

ü  110% = 100% + 10%

ü  100% of 36 = 36

ü  10% of 36 = 3.6

ü  110% = 36 + 3.6 = 39.6

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Show that 30% of 65 is the same as 65% of 30

 (30 : 100%) x 65 = 19.5

     (65 : 100%) x 30 = 19.5