engineering productivity

What's the best way to kill engineering productivity? Two words: brain teasers.

At lunch today, we were talking about interviewing and interview questions. Although we all agreed that most brain teasers did not make good interview questions, we were nonetheless diverted into the conversational black hole of asking brain teasers.

Question 1: There is an airplane with N seats and N passengers. The first person walks in and sits in a random seat. Each following person sits in his/her own seat if possible. If not, he/she sits in a random seat. What is the probability that the last person will sit in his/her own seat?

Question 2: There are 25 racehorses, but only 5 horses can race at a time. Assuming that every horse runs every race in exactly the same time, and each horse's race time is distinct, how many races does it take to determine which 3 horses are the fastest?

We did manage to solve both problems before leaving the cafeteria. Eventually.