Mental Math Strategies
+ and – to 18
• Counting On
8 + 3 = __ Start at 8 and count up 3 more, 9, 10,11
• Making 10
6 + 8 = __ Start with 8, add 2 from 6 to make 10, and 4 more equals 14
• Doubles
• Counting Back
15 – 3 = __ Start at 15 and count down 3 less, 14, 13, 12
• Think Addition to Subtract
13 – 5 = __ THINK: 5 + ? = 13…8
So, 13 minus 5 equals 8
Created by J.Anjos & K.Dennis (CTE) November 2007
Grade 1
Mental Math Strategies
+ and – to 18
• Making 10
6 + 8 = __ Start with 8, add 2 from 6 to make 10, and 4 more equals 14
• Doubles
• Building on a known double
Doubles plus one: 4 + 5 = __ THINK: 4 + 4 + 1
Doubles minus one: 4 + 5 = __ THINK: 5 + 5 – 1
Doubles plus two: 4 + 6 = __ THINK: 4 + 4 + 2
Doubles minus two: 4 + 6 __ THINK: 6 + 6 - 2
• Think Addition to Subtract
13 – 5 = __ THINK: 5 + ? = 13…8
So, 13 minus 5 equals 8
Created by J.Anjos & K.Dennis (CTE) November 2007
Grade 2
Mental Math Strategies
+ and – to 18
• Making 10
6 + 8 = __ Start with 8, add 2 from 6 to make 10 and 4 more equals 14
6 + 8 = __ Start with 6, add 4 from 8 to make 10 and 4 more equals 14
• Doubles
• Using the Commutative Property
If you know 9 + 3 then you know 3 + 9
Addition is commutative but subtraction is not
• Using the Property of Zero
►4 + 0 = 4
►0 + 8 = 8
►13 – 0 = 13
• Think Addition to Subtract
13 – 5 = __ THINK: 5 + ? = 13…8
So, 13 minus 5 equals 8
Created by J. Anjos & K. Dennis (CTE) November 2007
Grade 3 - 6
Mental Math Strategies
x and ÷ to 25
• Relate Multiplication to Repeated Addition
5 groups of 3 = 3 + 3 + 3 + 3 + 3 = 5 x 3
• Doubles
2 x 7 equals Double 7 or 7 + 7
• Five Facts
Skip Count by 5s
• Relating x to ÷
12 ÷ 3 = __ THINK 3 x ? = 12…4
So, 12 ÷ 3 equals 4
• Relate Division to Repeated Subtraction
8 ÷ 4 can be modeled by 2 groups of 4. So, 8 – 4 – 4 = 0
8 ÷ 2 can be modeled by 4 groups of 2. So, 8 – 2 – 2 – 2 – 2 = 0
Created by J.Anjos & K.Dennis (CTE) November 2007
Grade 3
Mental Math Strategies
x and ÷ to 81
• Skip Counting from a known fact
8 x 2 = __ THINK 6 x 2 = 12
Now skip count by 2s to get 8 groups of 2
12…14, 16
• Doubling (4 and 8)
For multiplying by 4: 7 x 4 = __ Double and double again. 7, 14, 28
For multiplying by 8: 5 x 8 = __ Double, double, and double again. 5, 10, 20, 40
• Doubling + one more group (3)
For multiplying by 3: 6 x 3 = __ Double and add one group. 6, 12 + 6 = 18
• Tripling and Doubling (6)
For multiplying by 6: 5 x 6 = __ Triple and double. 5, 15, 30
• Nifty Nines
For multiplying by 9: 7 x 9 = __ Multiply by 10 and take away one group
7, 70 – 7 = 63
The sum of the two digits in the product is always 9
You should be familiar with strategies from previous grades.
Created by J. Anjos & K. Dennis (CTE) November 2007
Grade 4
Mental Math Strategies
x and ÷ to 144
• Annexing then adding Zero
3 x 200 = __ THINK 3 x 2 and then add the same number of zeros
3 x 2 = 6 + (two zeros) = 600
• Using the Distributive Property
5 x 7 = (3 x 7) + (2 x 7)
Partition 5 into 3 + 2 and multiply each addend by 7
98 x 7 = (100 x 7) – (2 x 7)
• Doubling and Halving
For multiplying by 50: 6 x 50 = __
THINK Multiply by 100 and divide by 2
6, 600, 300
• Partitioning
4 X 27 = __
4 × 20 = 80
4 × 7 = 28
108
You should be familiar with strategies from previous grades.
Created by J.Anjos & K.Dennis (CTE) November 2007
Grade 5 -6