Here’s my thought:
Pick one number. Set it aside.
Pick a second number. If bigger than the first, keep it. If smaller, pick the third.
By discarding the first, you change the odds to 1/2. If the second is bigger than the first, we no longer care about the first, so the probability is 1/2 that the second will be bigger than the third. If the second is smaller than the first, we no longer care about the second, and the probability is 1/2 that the third will be bigger than the first.
TZK-738
(For those who are wondering, this is the license plate number of brandonsveit of Odem, TX, a streetracer whose plea for help getting his Camaro over 95 mph up to “130 at least” where he likes it eventually resulted in his thread getting deleted. If you google his handle you might be able to see the google cached copy of the thread.)
Apparently this selfsame Puzzler was presented almost exactly ten years ago, week of February 19th, 2001. And your description of the solution is the one that was accepted as correct at that time.
Check it out:
http://www.dartmouth.edu/~chance/chance_news/recent_news/chance_news_10.03.html#item3
Thanks. I didn’t listen to the show in those days, but I’m not surprised. I wonder if they’re even still alive. So glad I never contribute to NPR, except on April 15.