Count From A Number Upwards
Example: 6 + 3
Think “6 … 7, 8, 9”
Hint: start from the larger number.
Example: 2 + 6
2 + 6 is Harder: “2 … 3, 4, 5, 6, 7, 8”
6 + 2 is Easier: “6 … 7, 8”
So do 6 + 2 instead (you get the same answer).
Jump Strategy
We can also count by 2s or 10s, or make any “jumps” we want to help us solve a calculation.
Example: 4 + 12
Think “4 … 14 … 15, 16”
Adding Up To Ten
See if any numbers add to 10. They don’t have to be next to each other.
Example: 7 + 8 + 3 + 2 + 5
7+3 is 10,
8+2 is another 10, which makes 20,
Plus 5 is 25
Do The Tens Last
Break big numbers into Tens and Units, add the Units, then add on the Tens.
Example: 14+5
Break the “14” into Tens and Units: 10 + 4
Add the Units: 4 + 5 = 9
Now add the Tens: 10 + 9 = 19
Think “4 plus 5 is 9, plus 10 is 19”
Another Example: 14 + 12
Break into Tens and Units: 10 + 4 + 10 + 2
Add the Units: 4 + 2 = 6
Now add on the Tens: 6 + 10 + 10 = 26
Aim for Ten
When a number is close to ten we can “borrow” from the other number so it reaches ten.
| Example: 9 + 79 is only 1 away from 10 | |
| so take 1 from the 7: 9 + 1 + 6 and give it to the 9: 10 + 6 = 16Think “9 plus 1 is 10 … 7 less 1 is 6 … together that is 16” |
Example: 8 + 5
8+2=10, so lets take 2 from the 5: 8 + 2 + 3
and give it to the 8: 10 + 3 = 13
We can also move backwards to ten, by making the other number bigger as needed:
Example: 12 + 7
Reduce 12 by 2: 12 − 2 = 10
Increase 7 by 2: 7 + 2 = 9
12 + 7 = 10 + 9 = 19
Compensation Method
“Compensation” is where you round up a number (to make adding easier) and then take away the extra after you have added.
Example 19+16
It is easier to do 20 + 16 = 36
Then take away the extra 1 (that made 19 into 20) to get: 35
Example 395 + 126
It is easier to do 400 + 126 = 526
Then take away the extra 5 (that made 395 into 400) to get: 521
Double when the numbers are the same
Example 5 + 5 = 2 x 5 = 10
Double if the numbers are close, then fix
Example: 5 + 6 is nearly two 5s, but 6 is 1 bigger than 5, so:
5 + 6 = two 5s + 1 = 10 + 1 = 11
Example: 7 + 9 is like two 8s, but 7 is 1 smaller than 8, and 9 is 1 bigger than 8. So it is exactly two 8s because 1 smaller and 1 bigger cancel each other:
7 + 9 = “8 less 1” + “8 add 1” = two 8s = 16
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