well, i have never done more then 100 in a row and that was when i was about 12. But i know i can do about 67 in a minute.
I can only do around 40 times at one go. Maybe could reach around 200 per day if I seriously doing it.
When I was working out, I could do it 200 times. Now I don't workout and I have belly fat. I can do 25 times, probably.
Sit-ups are pretty easy I can do series of 100 each. There's a website called twohundredsitups.com that helps you get to 200 sit-ups in one series. It has a special training program that's worth checking out