Adding whole numbers means that we are combining numbers to form a total.
We call the total in addition 'the sum.' The sum always means addition, it is the total of when numbers are added together.
Let's look at an example: 3 + 4 = 7
The sum of 3 and 4 is 7.
The sum is what comes after the equals sign in an addition question.
What is the sum of 13 and 3?
Start at 13 and count 3 forwards.
The sum of 13 and 3 is 16