Percentage Error

    The grade that you earn on a test could be called you "percentage correct" because it is a measure of how may questions you answered correctly.  Scientists, however, are interested in the amount of error in their measurements.  The amount of error is commonly expressed as "percentage error."
 
        Formula for calculating percentage error:
                        Percentage Error = difference between your value and the correct value X 100
                                                                                  correct  value

Steps in calculating percentage error:
     1. Determin the difference between your value and the correct value.
     2.  Divide the difference in values by the correct value.
     3.  Multiply the quotient by 100 to change your answer to a percent.
     4.  Label your answer with a percent sign.

Sample problem:
    Question:  A student measured the length of his desk as 81 cm.  Later he found that i was actually 75 cm long.  What was his percentage error?
 
    Solution: Percentage = 81-75 X 100
                                            75

                                      = 6/75 X 100

                                      = (.08) X 100

                Percentage Error  =  8%

    Practice Problem  Solve the following problems using the form that was demonstrated in the sample problem

        1.  A student measured the mass of an object to be 187 grams but the correct mass was 170 grams.  What was the student's percentage error?