How to add up the programmers way – fast

Add down the first column = 5
then the next = 8 therefore 58 (easy ay!)

45
13
___
58

23
46
___
69

Same with 3 numbers!
345
234
___
579

And here you say 9+1=10 and write it, then the next number so you are half way through the number already….

985
111
___
1096