Transcript Adding and Subtracting Whole Numbers - MATH GR 3-5

Adding and Subtracting Whole
Numbers
Benchmark
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MA.2.A.2.1: Recall basic addition and related
subtraction facts.
MA.2.A.2.2: Add and subtract multi-digit whole
numbers through three digits with fluency by using a
variety of strategies, including invented and standard
algorithms and explanations of those procedures.
Objectives
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Review of basic subtraction facts.
Develop fluency with multi-digit addition and subtraction.
Subtraction
Subtraction Facts
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Subtraction is removing some objects from a group.
The meaning of 5 – 3 = 2 is "Three objects are taken
away from a group of five objects and two objects
remain".
Examples:
6-2=4
9-3=6
Subtraction Example
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Example: 8 - 3
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This is the subtraction of 3 from 8 or 8 minus 3
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Subtraction is represented as shown:
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We can count down to get the difference
8  7, 6, 5
so the difference is 5
3
8
-3
What is Subtraction?
Subtracting whole numbers is
the inverse operation of
adding whole numbers.
Relationship between Addition and
Subtraction
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There is an inverse relationship between addition and
subtraction.
If a math fact is considered, for example 3 + 7 = 10.
Then the following are also true:
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10 - 3 = 7
10 - 7 = 3
Similar relationships exist for subtraction, for example
10 - 3 = 7. Then the following are also true:
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3 + 7 = 10
7 + 3 = 10
Subtraction word problem
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A.
B.
C.
D.
Mika is 6 years younger than her cousin Ben. Ben is 11
years old, how old is Mika?
Mika is 5 years old
Mika is 6 years old
Mika is 4 years old
Mika is 7 years old
Subtraction facts
Subtractions with one digit are
usually fairly easy.
Things start getting complicated
when you have more than one
digit and you cannot remove the
number at the bottom from the
number on top such as when
doing 85 − 8
Two-Digit Subtraction
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What is 76 – 23?
Let’s use the 100 Chart
Two-Digit Subtraction (cont.)
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What is 76 – 23?
Start at 67.
23 is 2 tens 3 ones
Let’s count back in the 100 chart 2 tens and then 3 ones
Two-Digit Subtraction (cont.)
Examples
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83 – 50 = ____
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22 – 14 = ____
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46 – 15 = ____
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31 – 15 = ____
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73 – 26 = ____
Word Problem
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There were 32 birds in the trees. Then 15 birds flew
away. How many birds are in the trees now?
Break Apart Approach
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Breaking Apart makes subtraction easier.
Example:
63 – 7 = ___
7
3
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4
Subtract 3 to get 60. Then subtract 4 more.
63 – 7 = 63 – 3 – 4 = 60 – 4 = 56
Examples
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Use the Break Apart strategy to find the difference:
75 – 7 = _____
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82 – 5 = _____
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76 – 9 = _____
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85 – 8 = _____
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Subtraction by Regrouping
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What is 42 – 15?
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Step1: Are they enough ones to subtract 5?
No.
Step 2: Regroup 1 ten as 10 ones.
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Subtraction by Regrouping (cont.)
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Step3: Subtract the ones.
12 – 5 = 7
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Step 4: Subtract the tens.
3–1=2
Subtraction by Regrouping (cont.)
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The difference is then:
27
Example
Since you could not remove 8 from 5, you
borrowed a ten from 8 tens and add that to 5
to make it 15
Word Problem
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Jane and her mom made 33 puppets for the craft fair. By
noon, they had sold 14 of the puppets. How many
puppets did they have left to sell?
Solve the Following Problems
89
- 25
50
- 9
69
- 35
99
- 12