Percents

Percents are related to Decimals and Fractions.  They are all parts of whole amounts.  Percent means "per hundred".  Percents are out of the number 100. Each format can be converted to the other formats.  

The symbol for percentages is  %.

 

To convert from decimal to percent to fraction form, use the following rules:
Decimal Percent Fraction
Given:

  .55

 55%

Move the decimal point 2 places to the right

 55/100 = 11/20

put the decimal over the place value it is in (hundredth=100) and then reduce

.345(thousandths=1000)

345/1000=69/200 
.70 or .7

(end zeros may be left off)

move decimal point 2 places left

 Given:

70%

 70/100 = 7/10

 place the percent over 100 and reduce
.40 or .4

change it to a percent then take the top # off and move dec. pt. 2 places left

OR

divide the top number by the bottom number on your calculator

 40%

if it is not over 100 then get the fraction to n/100, the top # is the percent

 Given:

2/5
.375

divide the top number by the bottom number on your calculator

 37.5%

get the decimal for 1st and then move the dec. pt. 2 places right

 Given:

3/8
Given:

1.25

 125%

move dec. pt. 2 places right

(this is more than 100%)

 1 25/100 = 

1 1/4

the whole number stays a whole number, the decimal becomes the fraction
Given:

.005

 .5% OR 1/2%

(not even 1 %)

 5/1000 = 1/200

put the decimal over the place value

Finding percents of numbers:

20% of 500 is what?  (translate the words to an equation and solve )

.20 X 500 = n      (percent changes to a decimal, multiply and is means equals)

100 = n

 

65% of what number is 45    (translate the words to an equation and solve )

.65 x n = 45        (percent changes to a decimal, multiply and is means equals)

.65n=45                divide by .65

n=approximately 69.2%

 

 

What percent of 400 is 30?    (translate the words to an equation and solve )

n x 400 = 30        (percent changes to n since it is missing, multiply and is means equals)

400n=30     divide by 400

n=.075         move dec. pt. 2 places right

n= 7.5%

 

25 out of 500 is what percent?

25/500       change to a fraction & divide on the calculator

.05            change from a decimal to a percent

5%

 Sale Discounts: discounts are pieces that you save on a certain item(s)

15% off a shirt that costs $12.89 translate the problem to multiply
.15x 12.89 the percent by the original cost
$1.9335 round the answer to the 2nd decimal place
$1.93 this is the discount or amount you save
12.89-1.93 subtract the savings from the cost of the shirt
$10.96 sale cost of the shirt

Tax:  tax is an additional charge they add on to your bill

7% tax on the shirt you want to buy above translate the problem to multiply
.07x 10.96 the tax by the  cost
.7672 round the answer to the 2nd decimal place
$0.77 this is the tax that you add to the cost
10.96+.77 add the tax to the cost of your purchase
$ 11.73 final cost

Percent of Increase or Decrease: this is the percent of change that items go up or down 

% of increase or decrease= change in amounts DIVIDED by the original amount

A shirt costs $25.00 on Monday, on Tuesday it was $20.00, what's the percent of change? Obviously since it went down this is a percent of decrease problem 
change in amounts is 25 -20 = $5 subtract the 2 numbers
5/original  find the original amount (Monday is earlier than Tuesday)
5/25 then divide
.2 change the decimal to a percent
20% decrease  
  increase problems are done the same way!

Pie Charts / Circle graphs: This chart uses percents to compare area that each sector or slice of the circle has. For example The amount of money you spend on things during the year.

To make it easy lets assume your total Budget is $100.
Expense Amount out of total Percent
food 20/100 20%
clothing 50/100 50%
music 15/100 15%
movies 15/100 15%

Then, change each percent to a piece of the 360 degree circle. Do this by multiplying the decimal form of the percent by 360.
Percent Work Degree
20% .20 x 360 72
50% .50 x 360 180
15% .15 x 360 54
15 % .15 x 360 54

Then use a protractor to divide the circle into the correct degree sectors. Color each sector and label each sector with the PERCENT and Title in which the sector is representing. Don't Forget to give the Graph a TITLE!!!!!

 

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