Teaching Algebra with Manipulatives

Using Overhead Manipulatives
• Ask students how to determine by what percent the original figure was
increased or decreased. Y, 3 out of 8 sections were removed so the
figure was decreased by 3 8 or 37.5%; Z, 4 out of 8 sections were added
to the original figure, so the figure was increased by 4 or 50%
8
Extension
Modeling and Solving Percent of Change Problems
• Present the following problem.
The sale price of an item is 20% off the original price. Today only, the
store offers to take an additional 20% off the sale price. Are these two
discounts the same as 40% off the original price?
• Draw a 10-by-10 square on the dot
paper transparency. Tell students that
it represents the original price. See
Figure S. Ask them how to show a 20%
decrease. Remove 20 squares Label
the remaining section 80. See Figure A.
S
A
80
X
X
X
X
X
64
L
X
X
X
X
X
X
X
X
X
• Ask students how to calculate a 20%
decrease in the remaining section.
20% of 80 16 Remove 16 squares.
Replace the label 80 with 64. See
Figure L. “If the original cost was $100,
what was the final sale price?” $64
S
60
E
X
X
X
X
X
X
X
X
X
X
• Draw Figure E. Ask students what sale
price would result from a 40% decrease
in the original price. $60 Ask whether
a discount of 20% on a discount of 20%
of the original price is the same as a
discount of 40% on the original price. no
© Glencoe/McGraw-Hill 78 Teaching Algebra with Manipulatives