https://www.amazon.ca/Rapid-Math-Tricks-Tips-Number/dp/0471575631
He has two volumes.
There are tricks and techniques for this...
/u/The_Human_Empire, you might want to check out the various books such as https://www.amazon.com/Rapid-Math-Tricks-Tips-Number/dp/0471575631 to get you started. It's really just a matter of practice and training. The best thing would be to get a private tutor (which your parents would presumably be happy to pay for).
I suggest you get this book: http://www.amazon.com/Rapid-Math-Tricks-Tips-Number/dp/0471575631
It has a lot of them.