An Introduction to Percent

Kenneth Surdell                Lewis School
                               1431 N. Leamington
                               Chicago, Ill. 60651
                               312-804-3060

Objectives:

   Fifth grade students will develop a basic understanding that percent is a 
comparison of some number to 100. 
   Pupils will convert fractions to percent, percent to decimals and vice versa 
with a minimum of 90% accuracy. 

Materials:

 Per team: 2 sheets of 1cm2 graph paper; 2 pairs of scissors; 
 1 sheet of 100 squares. marked with 12% "A's". 16% "B's", 18% "C's",
 5% "D's", 3% "E's", 8% "F's", 13% "G's" and 25% "H's". 

Strategy:

   Develop the idea that percent is a comparison of some number to 100 which  
can be written in the form of x with the sign % or x%.  Think of the symbol % to 
be a distortion of the 100 in a ratio of x:100.  The ratio of 20 to 100 is 20 
percent or 20% and this is the same as 20 hundredths or 0.20. Therefore, 20 
parts per hundred can be renamed as 20/100, 20% or 0.20. 
   Show 50/100 as .50 as 50%. Follow up with 75/100, 30/100, 10/100, etc.  Have 
pupils rename other ratios of 100 as percent and decimal. 
   We know that 50/100 = 1/2, 75/100 = 3/4, 20/100 = 1/5 therefore we can show 
that 1/2 is 50%, 3/4 is 75% and 1/5 is 20%. 
   To convert fractions whose denominator is something other than 100, you must 
first rename the fraction with a denominator of 100. 
  
   Divide the students into teams of 3 or four.  Have one student in each team 
cut a 10cm by 10cm square off a graph sheet.  Count the number of sq. cm. in the 
square.  There are 100 sq. cm.  On chalkboard write this value as 100/100 = 
100%.  Point out that 100% is all of the squares or 100 squares. 
   Cut a second 10 by 10 square.  Compare it with the first.  They're equal.  
Now cut this second sheet in half.  Count the number of square cm. in each half. 
There are 50.  On the chalkboard show this as 50/100 = 50%.  Since 50/100 is 
half of the 100 original squares we can say that 50/100 = 1/2 which also equals 
50%. 
   Follow the above sequence and have the students cut out 25, 20, 10, 1 
squares.  Compare them to the original 100, write them as fractions of a 
hundred and convert the fraction to percent. 
  
   Use the graph sheet marked with letters "A" to "H".  Count the number of 
"A's".  Write as a fraction of 100 (12/100).  Convert to percent (12%).  
Continue the same procedure with the other letters. 
   Have teams make up a letter sheet of their own, exchange with other teams and 
determine the percent of each of the letters. 
   Pupils should be able to convert percent to a fraction with a denominator of 
100 and rename the fraction as a decimal.