# 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
• 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
• Method 3: subtracting by counting on
• Then count up until you get the first number

#### 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:
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)

b)

c)

• 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)

b)

c)

• 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 = ____