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					MATH AND STATISTICS "TOOLBOX RECIPE CARDS" FOR JOURNALISTS
How a percent is written:

Step-by-step in plain English
Need a math mentor? Click here for sources!
St. Petersburg Times MATH and STATISTICS TOOLBOX RECIPE CARDS • Ratio • Two classic Percent questions • Timed Math Drills (test your mettle) Note: electronic only DETAIL SHEETS • Reducing a fraction • Order of operations • Terminology and math style

percent:

15 percent 3.5 percent 0.5 percent 4%

Definition: A part of one hundred. Notes: A mathematician would also write a percent as a fraction 15/100 or decimal: .15. A percent written as a decimal or fraction is generally not the correct style for use in news copy but we will use both number forms to learn about math. To calculate with a percent you must first change it to one of two things: a fraction or a decimal.
Common Illustration: You and some friends go out to lunch and eat $100 worth of food. The group decides a 15 percent tip is fine. 15 percent = 15/100 = .15 so, .15 X $100 = $15 ... In this case, the tip is $15.

Two "Change" recipes:
A) to change a percent to a fraction; example: 25 percent to 25/100 or 25 percent to 1/4* Step 1. divide the percent (25) by 100; in this case, 25/100 Step 2. reduce the fraction, if you can, by dividing both the top (numerator) and bottom (denominator) by the same number; in this case, divide by 25 to change 25/100 to 1/4 ("25" can be divided into the numerator 1 time and into the denominator 4 times) *TIP: See the "Reducing a fraction detail sheet" for a list of standard questions that can help you decide if a fraction can be reduced. To be correct, a fraction should be expressed in its lowest possible form. It is also clearer to say or write "one-quarter" rather than "twenty-five one hundreths" or 25/100. B) to change a fraction to a decimal; examples: 25/100 to .25 or 1/4 to .25 Step 1. divide the top (numerator) by the bottom (denominator) Two longhand division math examples:

COMING ATTRACTIONS: § More percent questions including: markdown (decrease), markup (increase), percent of total and percent change § Millage rates § Percent and percentage points § Currency exchange rates § Mean, median & mode § Metric conversions § Consumer Price Index

25 25/100 = 100 = 100 25

Step 1 detail:

1 1/4 = 4 = 4 1

.25 100 25.00 200 500 500 0

(100 x 2 = 200) (100 x 5 = 500)

.25 4 1.00 8 20 20 0

(4x2 = 8) (4 x 5= 20)

So, 25/100 = .25

So, 1/4 = .25

Cards written and designed by Debbie Wolfe Technology Training Editor St. Petersburg Times 4th Floor News Training 490 First Avenue South St. Petersburg, FL 33701

dpwolfe@sptimes.com
3/1/2000

Step 2. To check your math, multiply the decimal by 100 to see if you get the original percent value and/or an equivalent. In the above examples, 25/100 is equivalent to 1/4. Equivalent fractions have the same decimal and percent values: .25 = 25/100 and .25 = 25/100 = 1/4 Longhand multiplication TIP: It is helpful to do "double check" example: the long-math method of 100.00 multiply the decimal by division so you do not x .25 100 to get the percent misplace the decimal point. Changing a percent to a decimal 50000 "in your head" can lead to 200000 Step 2 whopping mistakes especially if 250000 detail the percent is a single or triple digit number. 100. 00 adds up One common blunder is the . 25 as 4 places following: 5 percent = .5 Does it? Use longhand math to 25.0000 so, move the decimal double check the decimal. You will find 5 percent = 0.05 and point over 4 places 50 percent = .5! Really. in the final answer What about 12.5 percent? starting at the right and How can you make a decimal moving left out of a percent that already has a decimal? Easy, divide the It checks out, .25 = 25 percent! percent by 100 just like before: 12.5 percent = 12.5/100 = .125 Related: See the "Famous Shortcut" for changing decimals to percents and percents to decimals on the ratio card.


				
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