Hi everyone!

I'm a University Student in Germany, and we are getting ready to take our final exams. I come from the US, but am taking courses in German - so excuse me if the translation is a little bit funny (the questions are in German)!

Right now I'm doing a practice final exam, and I'm at a point where I have no clue where to start.

Here is the question:

3a) In the trainstation, there is a bench with 10 seats with 10 people sitting on it. From these 10 people, 2 don't have Tickets (illegal riders). In how many situations will the 2 without Tickets be sitting next to eachother?

3b) How many illegal riders do there have to be, so that there is a 99% probability that of 100 Riders, at least 1 is an illegal rider?

3c) 97% of all Riders have tickets. One Controller checks 5% of the Riders. The probability that one Rider is an illegal rider and who will be checked is 0.20%. Does the Controller have an eye for who is an illegal rider, or has he picked them out by chance?

3d) The probability that a rider is riding illegally is 5%. 200 controlls will be taking place. What is the probability that at least 7 and at most 12 illegal riders will be caught?

If anybody can give me any help on how to evenstart, I will be forever grateful!

Thank you

Melanie