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Subtraction strategies

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Intros
Lessons
  1. Introduction to Subtraction Strategies:
  2. Mental math and differences of 10
  3. Subtraction strategy #1: friendly number with adjustment
  4. Subtraction strategy #2: friendly number by adding to both numbers
  5. Subtraction strategy #3: counting on from the first number
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Examples
Lessons
  1. Subtracting by breaking up the subtrahend
    Subtract by breaking up the number being taken away.
    Fill in the blanks by following the example:
    Subtraction Strategies
    1. 57 - 9 = 57 - 7 - ____ = 50 - ____ = ____
    2. 64 - 7 = 64 - ____ - ____ = 60 - ____ = ____
    3. 38 - 9 = 38 - ____ - ____ = 30 - ____ = ____
    4. 92 - 8 = 92 - ____ - ____ = ____ - _____ = _____
  2. Subtracting by 9 strategy
    Subtract 9 by: subtracting 10 first, then putting 1 back
    1. 17 - 9 = ____
      17 - 10 = ____ + 1 = ____
    2. 42 - 9 = ____
      42 - 10 = ____ + 1 = ____
    3. 35 - 9 = ____
      35 - 10 = ____ + 1 = ____
  3. Subtracting by 8 strategy
    Subtract 8 by: subtracting 10 first, then putting 2 back
    1. 15 - 8 = ____
      15 - 10 = ____ + 2 = ____
    2. 63 - 8 = ____
      63 - 10 = ____ + 2 = ____
    3. 47 - 8 = ____
      47 - 10 = ____ + 2 = ____
  4. Subtracting using friendly numbers with adjustment
    Subtract by changing one number into a "friendly" number and adjust. Fill in the blanks.
    1. Subtraction Strategies
    2. Subtraction Strategies
    3. Subtraction Strategies
  5. Subtraction strategy: make friendly numbers by adding to both numbers
    Subtract: make "friendly" numbers by adding to both numbers. Fill in the blanks.
    1. Subtraction Strategies
    2. Subtraction Strategies
    3. Subtraction Strategies
  6. Subtraction strategy: counting on from the second number
    Subtract by counting on from the second number. Show your work.
    1. 573 - 252 = ____
    2. 408 - 126 = ____
    3. 847 - 639 = ____
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Practice
Topic Notes
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In this lesson, we will learn:

  • The subtraction strategy of: (1) using a friendly number with adjustment, (2) adding to both numbers to create a friendly number, and (3) counting on from the first number (subtrahend)
  • Understanding subtracting by 9

Notes:

  • Method 1: change into a "friendly" number then adjust (by adding)
    • Round one the number being taken away to the nearest multiple of 10
    • Then adjust by adding how much you rounded by to get the answer
Subtraction Strategies
  • Method 2: make "friendly" numbers by adding to both numbers
    • Add to one of the numbers so that it becomes the nearest multiple of 10
    • Add the same amount to the other number
Subtraction Strategies
  • Method 3: subtracting by counting on
    • Start with the number you're taking away (the second number)
    • Then count up until you get the first number
Subtraction Strategies