Lesson HOW TO - Percentage Increase

Source code of 'HOW TO - Percentage Increase'

This Lesson (HOW TO - Percentage Increase) was created by by longjonsilver(2297)

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About longjonsilver: I have a new job in September, teaching

Beyond the basics of percentages, a typical question would be along the lines of:

EXAMPLE: An item last year cost $450. If it increases this year by 15%, what is its new cost?

Long-winded solution, with explanation is as follows...

I shall find what 15% of 450 is and then add this onto 450. This will be the answer.

So, (15/100) * 450 = 67.5

Therefore, the new cost is 450 + 67.50 = 517.50.

Quick Solution (in one line):

1.15*450 = 517.50

The full explanation of this starts with the first solution from above, which is the original price plus the 15% of it:

450 + 0.15*450 ... NOTE the 0.15 (which is 15% in decimal form)

This can be written as 
1*450 + 0.15*450
(1+0.15)*450
1.15*450 = 517.50

The skill is reading the question and jumping to the last line.

EXAMPLE: A golf club last year cost $80. Its price is increased by 6%. What is the new cost of the club?

Well, 6% is 6/100 or 0.06 as a decimal, so 1 (the original) + the 0.06 will be the percentage increase:

1.06 * 80 = 84.8 Done!

In summary

Increase of  1%... multiply by 1.01
Increase of  2%... multiply by 1.02
Increase of  5%... multiply by 1.05
Increase of 10%... multiply by 1.10
Increase of 20%... multiply by 1.20
etc