How many people do you know?
1 - you must know their first name
2 - they must know your first name
3 - you must have met them at least once in real life
4 - you must have spoken to them at least once in real life
5 - you would both be able to recognise eachother on the street today
6 - you would talk to them on the street if you really had to
7 - they don't have to be friends - they can be people you hate
8 - you can include friends, family, workmates and even teachers (assuming they meet above criteria)
Take a (not so wild ) guess.
Through my own family and relative i probably know around 1200 people - possibly more - big family
Work colleagues probably around 300 from various jobs
Sccol/College/Uni - 200
Other friends about 60
So around 1770 - only a rough guess - if anything I probably know more.
Mind you the chances of me meeting a large chunk of these people ever again are small but I would certainly speak to them (and I always get randomers recognising me so its a fair bet to say all of them would remember me