Lesson HOW TO - Percentage Decrease

Source code of 'HOW TO - Percentage Decrease'

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

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

So, how about percentage decrease?

EXAMPLE: An item usually costs $450. It is reduced in a sale by 15%, what is its sale price?

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

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

So, (15/100) * 450 = 67.5

Therefore, the new cost is 450 - 67.50 = 382.50.

Quick Solution (in one line):

0.85*450 = 382.50

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

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
0.85*450 = 382.50

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

EXAMPLE: A golf club last year cost $80. Its price this year is reduced 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 reduction:

0.94 * 80 = 75.2 Done!

In Summary

Decrease of  1%... multiply by 0.99
Decrease of  2%... multiply by 0.98
Decrease of  5%... multiply by 0.95
Decrease of 10%... multiply by 0.90
Decrease of 20%... multiply by 0.80
etc