mental math strategies for grade 3
DESCRIPTION
I describe 5 Mental Math Strategies that students can use to help solve math equations.TRANSCRIPT
Mental Math Strategies
for Grade 3 Students
All photos Courtesy ofMS Clip Art
Roshel Salvador
What is Mental Math??
It’s the ability to solve math equations in your head….
WITHOUTusing
paper OR a pencil!
With Mental Math you can
manipulate (change) your
number to make an easier equation.
What’s an equation???It’s the number sentence.
Here are a few Mental Math strategies:
• Count on• Doubles• Near Doubles• Make a Friendly Number• Front-End Adding or
Expanded Notation
Count On:
If one of the numbers being added is a small number,then just count on.
Count On:
7 + 3 =
3 is a small number,so just count on
to get your answer.
Count On:
RULE:Usually, if one of the numbers are from 1 to 5, you can just count on.
Doubles:
Knowing your doubles can help you solve equations quickly!
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.
Near Doubles:
Knowing your doubles helps with the Near Doubles strategy
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
Near Doubles:
Examples of other near doubles:
11+13= 5+8=
11 + 11+2= 5 + 5+3
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
Make a Friendly Number:
What is a friendly number???
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
For example,
to make 28 a friendly number, I can add 2 to it to make it 30
Make a Friendly Number:
More examples:
• Add 5 to 35, to make 40
• Subtract 2 from 22 to make 20
Make a Friendly Number:
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:
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
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
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:
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
When you:• “give & take” adding• “give/give” subtracting• “take/take” subtracting
You are compensating!
Make a Friendly Number:
Front-End Adding
When you front-end add you use expanded notation or your place values.
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
• 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
Let’s Review the Mental Math Strategies
• Count on• Doubles• Near Doubles• Make a Friendly Number• Front-End Adding or
Expanded Notation