Information for Parents – Grade 4 Mental Math Strategies
Basic addition and subtraction facts to 18
**by the end of grade 3, students should have quick recall of the facts and successfully
complete a one minute drill of mixed facts (12).
To help your child:
Addition strategies:

Start with the doubles and make sure they know them quickly and accurately: 2+2=4,
6+6=12, 8+8=16, etc.

Next, work on doubles plus one, then doubles plus two:
For example: 7 + 8 – They should know 7+7=14, so simply add one more and get 15.
6 + 8 – They should know 6+6=12, so add two more and get 14.

Partner numbers to ten: 5+5, 6+4, 7+3, 8+2, 9+1
Students should know these automatically in grade 4. Once they know these, it will help
them with questions like 6+5 – If 6 and 4 make 10, then just add one more and get 11.
This will also help them with some of the partner numbers to 100. 50+50, 60+40,
70+30, 80+20, 90+10

Other partner numbers to 100 : 25+75, 50+50, 30+70, 55+45, 65 + 35
Subtraction strategies:

Count back if the number is small: 12 – 3, 11, 10, 9. I counted back 3 and landed at 9,
so the difference is 9.

Count on if the numbers are close: 13 – 9, 10, 11, 12, 13, I added on 4, so the
difference is 4.

Think addition! Many students find that turning the subtraction fact into an addition fact
makes it easier.
For example, 16 – 9 think 9 + what? = 16. “ I know 9 + 7 = 16, so my difference is 7
Mental Addition Strategies (with larger numbers):
**students are required in grade 3 to show how they would add two digit numbers mentally. In
grade 4, this extends to larger numbers. They are also required to show their thinking. Below
are some mental addition strategies:
Front-end Addition (adding left to right) :
268 + 415, add the hundreds, then the tens, and last the ones. Next, add these sums all
together.
200 + 400 = 600, 60 + 10 = 70, 8 + 5 = 13, add 600 + 70 + 13 = 683
Compensation :
238 + 596 – if we can make friendly numbers by adding an amount to one number and
subtracting that amount from the other number, the sum won’t change.
+4
238 + 596 so 234 + 600 = 834
Mental Subtraction Strategies (with larger numbers):
6498 – 1237
Number Line Strategy :
+3
+60
1237 1240
+700
1300
+4000
2000
+400
6000
6400
+90
+8
6490 6498
1-First, draw a number line.
2-Next, write the LEAST number on the LEFT hand side of the number line and the
GREATEST number of the RIGHT hand side of the number line.
3-Then, you have to make “smart jumps” to get from the least number to the largest
number.
4-As you jump, record the number that you are adding to make the smart number on the
top of the number line with a plus sign beside it. This will help you to remember to add
these numbers together once you are finished jumping.
5. Once you have made it to the greatest number, add up all the numbers on the top of
the number line together to get your total DIFFERENCE.
Birthday Strategy (constant difference) :
428 – 197 – if we can make friendly numbers by adding or subtracting an amount to one
number and adding or subtracting the same number from the other number, the difference
won’t change.
+3
+3
438 - 197 so 431 – 200 = 231
(This one is called the birthday strategy because we relate it to our ages and our brothers’ and
sisters’ ages.
If I am 10 and my sister is 13, we are three years apart.
When I am 40, my sister will be 43. We’ll still be three years apart. The difference between our
ages is constant.)