Doubling

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Doubling Halving with Multiplication
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• Doubling and halving works because of the
  relationship between multiplication and division.
  
• Since multiplication and division are opposites,
  we can multiply one factor by 2 and divide the
  other factor by 2 and the product does not change.

3

• This method of multiplication works well with
  some numbers. Numbers that are multiples of 5
  and 10 work well.
• Since it is more difficult to compute with
  fractions and decimals, it works best to take
  half of an even number. With some experience,
  students soon find which numbers work nicely with
  this method.

4
64 x 25 ?

• 64 x 25 I can easily take half of 64 and
  double 25.
• 32 x 50 I can easily take half of 32 and
  double 50.
• 16 x 100 I can easily find this product!
• 16 x 100 1600

COOL
5
Try one on your own

• Choose a problem from these
• 33 x 55
• 45 x 36
• 5 x 148

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Did you choose this? 5 x 148

• 5 x 148

I can easily double 5.
I can take half of 148.
x
10
74
Now its easy with 10.
How did you do?
7
Doubling and Halving

• This method of multiplying supports mental
  math. This method also supports the properties
  of multiplication and division. Students feel SO
  powerful when they can use this!