Nice little cheat sheet you came up with there.

Another common one you should add to the list is how to find the percentage of a number.

Ex. What is 24% of 80?

.24*80= 19.2

edit: ah, I guess you already have one similar in "Finding a percentage of a quantity". Dunno how I missed that.

# Percentages

Percentages

Changing a percentage to a decimal

Divide it by 100.

Eg:

17.25% goes to

17.25/100 = 0.1725

Changing a percentage to a fraction

Times it by 1/100

Eg:

3 and 1/3% goes to

15/4% goes to

15/4 * 1/100 goes to

3/4 * 1/20 = 3/80

Changing a decimal to a percentage

Times it by 100%

Eg:

0.27 * 100% = 27%

Changing a fraction to a percentage

Divide the numerator by the denominator and times by 100%

Eg:

3/8 goes to

0.375 * 100%

= 37.5%

Finding a percentage of a quantity

Either -

press the amount * the percent amount and hit the % button

or -

change the percent to a decimal and times it by the quantity

Eg:

7 and 3/4% of 84.35 goes to

0.0775 * 84.35 = 6.54

Expressing as a percentage

percentage of an amount to an another amount.

amount a divided by amount b times 100%

Eg:

1000kg of 2000kg goes to

1000/2000 * 100%

50%

Percentage change

decrease or increase

change in value/original value * 100%

Eg decrease:

O price = 6.10

new price = 5.30

change in value = 6.1 - 5.3 = 0.8

0.8/6.1 * 100%

= 13.11%

Eg increase:

O prince = 18000

new price = 21000

change in value = 3000

3000/18000 * 100%

= 16.67%

Finding new price

increase or decrease

find the percentage, add or take to/from original price.

find original price

let the original price be x. Use algebra.

Eg:

falls 16% to $30

x - 16% of x = 30

x - 0.16x = 30

(1 - 0.16)x = 30

0.84x = 30

0.84x/0.84 = 30/0.84

original price = $35.71

Profit and loss

profit/cost price * 100

loss/cost price * 100

Eg:

cost price = $125

sell price = $165

profit = $165 - $125 = $40

40/165 *100% = 24.24% profit

**7 blog comments below**

Is it correct to say:

25% = 0.25

?

If we treat % as a variable and solve the equation we get

% = 0.01

This seems valid. Is this a common thing to do?

25% = 0.25

?

If we treat % as a variable and solve the equation we get

% = 0.01

This seems valid. Is this a common thing to do?

**Peterssidan**on Mon Nov 21, 2011 5:27 pm

Peterssidan wrote: |

Is it correct to say:
25% = 0.25 ? If we treat % as a variable and solve the equation we get % = 0.01 This seems valid. Is this a common thing to do? |

lol. nice one.

That is also because per cent means every one hundred. So yeah % = 1/100 = 0.01.

**loremar**on Mon Nov 21, 2011 5:36 pm

Quote: |

Is it correct to say:
25% = 0.25 ? |

Yep. To change a percentage into a decimal, you just put the decimal in front of the percentage. Or in mathematical terms, just divide the percentage by 100.

25/100=0.25

**Ghost Rider103**on Mon Nov 21, 2011 6:26 pm

25% = 0.25 makes sense...

If you think of 100% as 1 (whole),

25% is 25/100 is 1/4 of 1 (whole)

1 divided by 4 is 0.25, 4 groups of 0.25 will make 1 (whole).

1% goes to 1/100 goes to 0.01, that makes sense.

If you think of 100% as 1 (whole),

25% is 25/100 is 1/4 of 1 (whole)

1 divided by 4 is 0.25, 4 groups of 0.25 will make 1 (whole).

1% goes to 1/100 goes to 0.01, that makes sense.

**Hello_World**on Tue Nov 22, 2011 7:58 am

Well what you just said complicates things.

I understand what you mean. But for me, when learning, I like to just stick to the basics. Divide the percentage by 100 to get the decimal. Done.

I understand what you mean. But for me, when learning, I like to just stick to the basics. Divide the percentage by 100 to get the decimal. Done.

**Ghost Rider103**on Tue Nov 22, 2011 3:38 pm

Hmmm... that is an interesting comment.

I suppose that you are correct, it does complicate things somewhat.

But for myself, I find I retain better if I can fit things into a bigger picture in some small way.

Then if I forget the procedure, sometimes I can figure it out backwards.

It does mean that everything I try to learn seems to take longer, and that I don't understand the weirdest stuff (according to others). (Stuff which may be a simple procedure but I can't fathom why I am trying to do it in the first place..)

I suppose that you are correct, it does complicate things somewhat.

But for myself, I find I retain better if I can fit things into a bigger picture in some small way.

Then if I forget the procedure, sometimes I can figure it out backwards.

It does mean that everything I try to learn seems to take longer, and that I don't understand the weirdest stuff (according to others). (Stuff which may be a simple procedure but I can't fathom why I am trying to do it in the first place..)

**Hello_World**on Tue Nov 22, 2011 10:37 pm

Ghost Rider103on Mon Nov 21, 2011 4:45 pm