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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