The easiest addition of all is adding single digit numbers. The basis of this technique is to break down all numbers into multiple single digit problems. It can be used for adding numbers of all sizes.
This fundamental technique can be used to add numbers large and small. Once mastered it will help speed up all other trick calculations.
Example
627 + 464 = 1091
Step 1
Split the problem into it’s hundreds, tens, and ones place problems. This will turn the original problem in to several one digit addition problems (with some easy to add zeros).
600 + 20 + 7
400 + 60 + 4
Step 2
Add each separate problem.
600 + 400 = 1000
20 + 60 = 80
7 + 4 = 11
Step 3
Add the resulting answers from step 2. They should be easy to add since they are again essentially one or two digit problems.
1000 + 80 + 11 = 1091
Practice mentally splitting, regrouping and adding large numbers and you will get fast at it.