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Using Know Facts to Find Unknown Facts

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Using Know Facts to Find Unknown Facts Powered By Docstoc
					Using Know Facts to
Find Unknown Facts
Math
3.3
Objective

  Use the distributive property to
   find products by breaking
   unknown facts into known facts
  Vocabulary

 Distributive Property – breaking apart
  problems into two simpler problems

 Example: (3 x 21) = (3 x 20) + (3 x 1)
 Investigating the Concept
 Two-Tone Rectangles
 Need Centimeter Grid Paper (T.T. 6);markers
 Outline two 4-by-6 rectangular arrays on the
  grid paper.
 Shade the first grid in one color.
 What multiplication fact does this array show?
 Color the second array so that it makes two
  arrays: one 4-by-5 and the other 4-by-1
 What multiplication facts do these arrays
  show?
Arranging the Facts
  Need Red and Blue Construction paper
  Hang a 5-by-6 array of red sheets of
   construction paper on the board.
  What multiplication fact does this array show?
  I need a volunteer to cover the last column with
   pieces of blue construction paper.
  What multiplication fact do the red sheets now
   show?
  What is the sum of the red and blue sheets of
   paper.
How can I break apart
facts?
  The distributive property
   shows that you can break
   apart facts to find the
   product.
Distributive Property
 3x5=2x5+1x5

 5 stays the same but the 3 is broken apart to 2
  and 1.
 Example
 (3 x 6) = (2 x 6) + (1 x 6)
 Why would you want to break apart 3 x 6
 2 x 6 = 12
 1x6=6
 12 + 6 = 18
 So 3 x 6 must equal 18

				
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posted:10/7/2011
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