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Percent of a number: Change the percent to a decimal and then multiply by the number.
Example: What is 5% of 9000.  Change 5% to a decimal by moving the decimal two places to the left and dropping the percent sign.  5% becomes .05.  Multiply .05 x 9000.  .05 x 9000 = 450.


Percent change - The amount that a value has changed, expressed as a percentage of the original value.
Percent change =     change in value   x 100
                             original value
The percent change may be an increase or decrease.  The change in value is expressed as a positive numbers.
 
Percent increase example:
A school with 750 pupils receives funding for an additional 75 students.  What is the percent increase in funding?
Change in value = 75 increase.


Percent increase =  75    x 100 
                           750 

                                   =    1   x  100  
                           10
                                   =  100   
                           10  

                        = 10 % increase
Percent decrease example:
One year a factory produced 60 cars per worker.  The following year the factory produced 57 cars per worker.  What is the percent decrease?
Change in value = 60 - 57 = 3 decrease.

Percent decrease  =    3    x  100
                               60
                         =    1    x  100
                              20
                         =   100 
                               20
                         =  5% decrease


Simple interest : Interest that is earned or paid only on the principal without including any earlier interest earned.  The amount that earns interest does not change.


Simple interest =   Principal x Rate x Time  
                                     100


Simple interest example:
If a person invests $500 at an interest rate of 4% per year, what is the amount of interest earned each year?


Simple interest =    500 x 4 x 1   
                               100
                     =    2000  
                            100
                     =  $20 each year.



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