All engineers are mathematicians, who enjoy puzzles. Probability theory is a stock part of the curriculum, so...
A theater has 15 seats in the first row. Patrons enter in single file, taking each consecutive seat, as they arrive. In this particular case, there are 8 boys, 7 girls.
If a boy and girl occupy adjacent seats, we have a candidate match. If boy sees girl on each side, that's two matches. Clearly, any possible arrangement will contain 1...14 candidate matches.
What's the average number of matches, for this row?
I found this in a book of math problems, it's a nice little exercise. However, my motivation here is mainly due to the fact that the author's reasoning, in his solution, is severely flawed. I think.
Take a crack at it. In a few days, I'll post the book solution, with my critique. Then you tell me where I'm wrong.
Or, if I'm right, yet somehow the book's solution is numerically correct, we have the challenge of explaining that miracle. Which is more interesting than the problem itself -