Addition Calculations
Some addition calculations can be done in your head, using a mental method.
In numbers under one hundred, we can just break it down into tens and units
and add them separately.
For example, if you had a pair of two digit numbers and the units added up to
10, that might easier to do in your head than write down.
Example 1. Let’s say we got a sum as a question. 56 + 74 =? We know that 6 + 4 = 10 so all we have to do in our heads is 50 + 70 = 120 Then we can do 120 + 10 = 130 and that’s our answer! 
For bigger numbers, it might be easier for us to do a written method of
addition. This might be column addition or using a number line.
Example 2. Let’s use an example so show to use a number line and the column method.235 + 147 =?In a number line, we start on the biggest number and count onwards. In a column method, first we have to line up the numbers in the correct place value, then add the columns, starting from the left.

We can also use subtraction to help us work out the answer to an addition
question. If there is a question with a missing number (like 6 + ? = 9), we
can use the answer and minus the value we do have ( 9 – 6) and we
should find our missing value (it’s 3).
We can check whether it’s right but putting the missing value into the original
sum and seeing if we get the correct answer. It works with bigger numbers
too!.
Example 3. Let’s say that the question we get it 78 +? = 114We can rearrange this into 114 78 = ?The answer is 36! We can now check this by putting 36 into the original question. 78 + 36 = 114 It works so 36 must be the correct answer. 
Related Topics
Placevalue Ordering Numbers Polygons
Rounding Numbers Quadrilaterals SubtractionCalculations