Percentages

how to work out percentages.

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  • Created by: Kelly:)
  • Created on: 30-05-11 18:11

Finding out a percentage of a number

say you were asked to find 85% of 65, you could find out:

  • 10% = 6.5
  • 80% = 52
  • 5% = 3.25

so 52 + 3.25 = 55.25

non-calculator method

or alternatively, you could simply:

65 * 0.85 = 55.25

calculator method

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Increasing amounts

to increase a number, say 40 by 20%, you could find:

  • 10% = 4
  • 20% = 8
  • 40 + 8 = 48

non-calculator method

or alternatively, you could:

40 * 1.2 = 48

calculator method

remember when increasing by 5% for example, you must type in 40 * 1.05!

and remember at the end of a question, if the answer is the percentage, don't leave it as the decimal :)

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Compound interest

compound interest is a little different. 

if you earn 2% compound interest each year then the amount increases a little bit each time because after the 1st year you would take 2% of the whole amount (including last year's interest).

an easy way to solving this is:

£125 in the bank increases by 6% compound interest for 5 years.

125 * 1.06^5

1.06 is the percentage increase and the number acting as the indices is the number of years.

:)

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Comments

Former Member

there are formulas for working out compound interest too.

(1+R_100)to the power of n

n=number of years and R is the percentage.

you times this by the original number to get the answer...

daviesg

Looking at both calculator and non-calculator methods to solve percentage problems, a good set of examples

q5773

ok

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