Mental Math
Strategies
for Grade 3 Students
All photos Courtesy of
MS Clip Art
Roshel Salvador
What is Mental Math??
It’s the ability to solve math
equations in your head….
WITHOUT
using
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
Near Double
2 + 2+1
Doubles
Doubles
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=
13-2 + 13
13+13 - 2
5+8=
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
Make a Friendly Number:
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 solve
because I’m working with a
friendly number.
Make 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
Make a Friendly Number:
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
(give 1) +1
-1
(take 1)
10 + 3= 13
New equation
Make a Friendly Number:
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”:
9 – 4= 5
(give 1) +1
+1
(give 1)
10 – 5= 5
11 – 4= 7
(take 1) -1
-1
(take 1)
10 – 3= 7
New equation
New equation
Make a Friendly Number:
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.
Front-End Adding
Expanded Notation is breaking your
number into ones, tens and hundreds
Eg. 58
5 tens, 8 ones
50 + 8
42
4 tens, 2 ones
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 number
70 + 9 = 79
Let’s Review the Mental Math
Strategies
•
•
•
•
•
Count on
Doubles
Near Doubles
Make a Friendly Number
Front-End Adding or
Expanded Notation