I have been very lucky to understand how to do arithmetic mentally, but maybe some people haven't been as lucky. Here is a simple example for a young child to understand an addition problem. By the way, mental math really only involves thinking about the nearest 5 or nearest 10.
Say we have the problem 7+8=
Mental arithmetic can become easier if you practice and just think about how close the digits are to an easier number to work with. For example 63+19: Separate into 60 and give the 3 to the 19 to be 22 and now the problem is 60+22.
I hope you enjoyed the addition mental math session!
How are you when it comes to doing arithmetic? Can you do it mentally or do you need to write everything down? Or do you pull out a calculator?