I'm trying to understand the Trading strategies in existence. Trading strategy various from person to person. Approximately how many traders would use own strategy? Is there a way to calculate the same?
"Strategy" is a very broad term. I haven't taken a survey, but I suspect that few investors take some strategy out of a book and follow it to the letter. Most people are going to adapt it to their own situation, modify it to suit their own risk preferences, modify it where they think they have a better idea (rightly or wrongly), etc.
Think of anything else you might do in life. When you look for a job or buy a car or go on a date, do you use your "own strategy"?