Lesson for Multiplying and Dividing Fractions with Post It Notes

Robert Foote                   Disney Magnet School
                               4140 N. Marine Drive
                                Chicago IL 60613
                                (773)534-5844

Objectives:

Students will use postit notes to measure various dimensions of rectangles to 
nearest fraction of an inch.  This lesson is intended for seventh grade.  
Students will divide fractions to predict the number of postits needed to meet 
the length and width of the rectangles. 

Materials Needed:

3 by 3 inch postit notes
1 1/2 by 2 inch postit notes
different sized rectangular shaped paper
rulers and yardsticks

Strategy:

Show students a piece of 8 1/2 by 11 inch piece of paper.  Ask students how many 
postit notes it would take to meet the length and width of the piece of paper of 
each size.  Explain the algorithm for dividing fractions to see mathematically 
how many 3 by 3 postits will fit and how many 1 1/2 by 2 will fit.  To 
illustrate this, divide 8 1/2 by 3.  You get 2 5/6.  Take the 3 by 3 postit 
notes and place them along the 8 1/2 side of the paper.  Carefully cut the 
overlapping part of the last postit note.  Measure the part remaining on the 
paper and it should be close to 5/6 of 3 or 2 1/2.  Measure the part you cut and 
it should be 1/2.  Do the same procedure with the other dimension of the 8 1/2 
by 11 paper by dividing 11 by 3.  Place the postit notes along the 11 inch side 
and verify the math.  Then do the same with 1 1/2 by 2 inch post it notes. After 
finishing this demonstration, pass out two different size rectangular sheets of 
paper and have students measure the sides.  Working in groups, have students 
determine mathematically how many of each kind of postit notes it would take to 
cover both dimensions of both sheets.  The students, after doing the math, will 
then tell you how many postit notes they need.  Give them exactly what they ask 
for and have them cut out the fractional part of the post it note they need by 
measuring it first.  Display the student's work on the board and discuss 
strategies for finding the answer and ways the answer could go wrong.  Precise 
measurement is very important for accurate results.  

Performance Assessment:

This activity in itself is a wonderful performance assessment.  You may modify 
the sizes of the rectangles or simply use straight lines.