Mental math can be as simple as counting 123.
First you need to know the secret of mental math.
But knowing the secret is not enough.
You must keep on practicing the skill until a habit of performing mental calculation is created in your subconsinous mind.
This app will give you the tools to practice mental math.
Practice makes perfect.
Think of it as learning bicycle. You must keep on practicing until you get the skill. Once you get the skill, you don't need to think how to balance your body in your head. It automaticlly adjust itself in your subconsinous mind.