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Unit 2: Using Mental Math

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Unit 2: Using Mental Math

  1. 1. Math 6:Whole Numbers Using Mental Math to Add
  2. 2. Getting started  70 + 89 + 30  What mental strategy did you use to solve the expression?  572 – 131  What mental strategy did you use to solve the expression?  4 x 33  What mental strategy did you use to solve the expression?  5 x 18 x 20  What mental strategy did you use to solve the expression?
  3. 3. Connect –Ways to Use Mental Math  Use mental math to add  Rearrange and use compatible numbers.  Compatible numbers are pairs of numbers that are easy to calculate.  For example, add 60 + 35 + 40  You would first add 60 + 40 = 100  Then add 100+35 = 135.
  4. 4. Ways to Use Mental Math  Use Mental Math to Subtract  687-464  When no regrouping is needed, start subtracting from the left.  Use Mental Math to Multiply  Rearrange and use compatible numbers.  4 x 19 x 25  =(4 x 25) x 19  =100 x 19  =1900
  5. 5. Ways to Use Mental Math  Use Mental Math to Multiply: 6 x 27  Break one of the numbers apart to make numbers that are simple to work with.  27 = (20 + 7)  (6 x 20) = 120  (6 x 7) = 42  120 + 42 = 162
  6. 6. In class work  pg. 51 #1-3 a, c, f, and 4, 5, 8
  7. 7. Homework  pg. 22 + 23

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