Mental Math

How can Mental Math help you solve equations?

What does it mean to do mental math?Definition: Mental math: Calculations that are done in a student's head without the guidance of pencil and paper, calculators or other aids. Mental math is often used as a way to calculate and estimate quickly, using math facts that a student has committed to memory, such as multiplication, division or doubles facts.

Common Mental Math:

• Count on• Doubles• Friendly Numbers• Front-End Adding or

Expanded Notation

Count On:If one of the numbers being added is a small number,then just count on..

8 + 4 =4 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:Doubles are when you take a number

and add it to itself. Knowing your doubles can help you solve equations quickly!

Examples: 2+2= 9+9= 15+15= 25+25=

You double the number.

Friendly Numbers: A friendly number is a number that ends

with a “0”.When numbers have a “0” in the ones spot; they are easier to add.

Example:

*to make 37 a friendly number, I can add 3 to it to make it 40

Examples:*to make 45 a friendly number,I can add 5 to itto make 50 *to make 22 a friendly number,I can subtract 2 from itto make 20

Friendly Numbers:

This is how friendly numbers help:27 + 5=

If I make 27 into a 30,30 + 2=

it is easier to solvebecause I’m working with a

friendly number.

Friendly Number Equation:

Notice how I changed the equation to 30 + 2, NOT 10 + 5

Friendly Number Equation:

I had to manipulate the equation by subtracting the (3) from the number being added (5) that I

moved to (27) to make (30).Otherwise, I’m just make a new and different

equation that won’t give the same answer

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• Friendly Numbers• Front-End Adding or

Expanded Notation