mental math strategies for grade 3
DESCRIPTION
I describe 5 Mental Math Strategies that students can use to help solve math equations.TRANSCRIPT
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Mental Math Strategies
for Grade 3 Students
All photos Courtesy ofMS Clip Art
Roshel Salvador
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What is Mental Math??
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It’s the ability to solve math equations in your head….
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WITHOUTusing
paper OR a pencil!
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With Mental Math you can
manipulate (change) your
number to make an easier equation.
What’s an equation???It’s the number sentence.
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Here are a few Mental Math strategies:
• Count on• Doubles• Near Doubles• Make a Friendly Number• Front-End Adding or
Expanded Notation
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Count On:
If one of the numbers being added is a small number,then just count on.
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Count On:
7 + 3 =
3 is a small number,so just count on
to get your answer.
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Count On:
RULE:Usually, if one of the numbers are from 1 to 5, you can just count on.
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Doubles:
Knowing your doubles can help you solve equations quickly!
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Doubles:
Doubles are when you take a number and add it to itself.
Eg. 2+2=9+9=15+15=25+25=
You double the number.
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Near Doubles:
Knowing your doubles helps with the Near Doubles strategy
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Near Doubles:
Near Doubles almost looks like a double, but it is off by 1,2,3 or 4
Doubles
2 + 2+1
Doubles
Near Double
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Near Doubles:
Examples of other near doubles:
11+13= 5+8=
11 + 11+2= 5 + 5+3
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Near Doubles:
You can even use subtraction for near doubles.
11+13= 5+8=
13-2 + 13
13+13 - 2
8-3 + 8
8+8 - 3
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Make a Friendly Number:
What is a friendly number???
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Make a Friendly Number:
A friendly number is a number that ends with a “0”.
Numbers with a “0” in the ones spot are easier to add with
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For example,
to make 28 a friendly number, I can add 2 to it to make it 30
Make a Friendly Number:
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More examples:
• Add 5 to 35, to make 40
• Subtract 2 from 22 to make 20
Make a Friendly Number:
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This is how it helps:9 + 4=
If I make 9 into a 10,10 + 3=
it is easier to solvebecause I’m working with a
friendly number.
Make a Friendly Number:
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BUT….
Notice how I changed the equation to
10 + 3, NOT 10 + 4
Make a Friendly Number:
I had to manipulate the equation.
Otherwise, I’m just make a new and different equation that won’t give the same answer
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In adding, it is called “give and take”.
If you give to one side, you have to take from the other side.
Make a Friendly Number:
9 + 4= 13+1 -1
(give 1) (take 1)
10 + 3= 13 New equation
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In subtracting, it is called “give/give” or “take/take”.
If you give to one side, you have to give to the other side.
If you take from one side, you have to take from the other side.
Make a Friendly Number:
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Some examples of “give/give” and “take/take”:
Make a Friendly Number:
9 – 4= 5+1 +1
(give 1) (give 1)
10 – 5= 5 New equation
11 – 4= 7-1 -1
(take 1) (take 1)
10 – 3= 7 New equation
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When you:• “give & take” adding• “give/give” subtracting• “take/take” subtracting
You are compensating!
Make a Friendly Number:
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Front-End Adding
When you front-end add you use expanded notation or your place values.
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Expanded Notation is breaking your number into ones, tens and hundreds
Eg. 58 425 tens, 8 ones 4 tens, 2
ones50 + 8 40 + 2
Front-End Adding
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• Front-end adding is when you start adding from the left and move to the right
Eg. 34 + 45 - start with the tens: 30 + 40 =
70- now the ones: 4 + 5 = 9
Now you`re working with a friendly number70 + 9 = 79
Front-End Adding
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Let’s Review the Mental Math Strategies
• Count on• Doubles• Near Doubles• Make a Friendly Number• Front-End Adding or
Expanded Notation