Subtraction strategies

Subtraction strategies

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

Lessons

  • Introduction
    Introduction to Subtraction Strategies:
    a)
    Mental math and differences of 10

    b)
    Subtraction strategy #1: friendly number with adjustment

    c)
    Subtraction strategy #2: friendly number by adding to both numbers

    d)
    Subtraction strategy #3: counting on from the first number


  • 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
    a)
    57 - 9 = 57 - 7 - ____ = 50 - ____ = ____

    b)
    64 - 7 = 64 - ____ - ____ = 60 - ____ = ____

    c)
    38 - 9 = 38 - ____ - ____ = 30 - ____ = ____

    d)
    92 - 8 = 92 - ____ - ____ = ____ - _____ = _____


  • 2.
    Subtracting by 9 strategy
    Subtract 9 by: subtracting 10 first, then putting 1 back
    a)
    17 - 9 = ____
    17 - 10 = ____ + 1 = ____

    b)
    42 - 9 = ____
    42 - 10 = ____ + 1 = ____

    c)
    35 - 9 = ____
    35 - 10 = ____ + 1 = ____


  • 3.
    Subtracting by 8 strategy
    Subtract 8 by: subtracting 10 first, then putting 2 back
    a)
    15 - 8 = ____
    15 - 10 = ____ + 2 = ____

    b)
    63 - 8 = ____
    63 - 10 = ____ + 2 = ____

    c)
    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.
    a)
    Subtraction Strategies

    b)
    Subtraction Strategies

    c)
    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.
    a)
    Subtraction Strategies

    b)
    Subtraction Strategies

    c)
    Subtraction Strategies


  • 6.
    Subtraction strategy: counting on from the second number
    Subtract by counting on from the second number. Show your work.
    a)
    573 - 252 = ____

    b)
    408 - 126 = ____

    c)
    847 - 639 = ____