There's no such thing as the sum of one number. "Sum" is what you have
when you moosh two numbers together into one by adding them.
For example:
If you put 5 pennies into your pocket, and then later, you put 3 more pennies
into there, what's in your pocket now ? Don't look, do it in your head.
You said there are 8 pennies now. That's correct. How did you figure it out ?
You 'added' 5 and 3 and you got 8 . 8 is the 'sum' of 5 and 3 .
