Mental Math Strategies for Grade 3

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???


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


More examples:

• Add 5 to 35, to make 40

• Subtract 2 from 22 to make 20


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.


BUT….

Notice how I changed the equation to

10 + 3, NOT 10 + 4


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.


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.


Some examples of “give/give” and “take/take”:


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!


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

Education

Mental Math Strategies for Grade 3