1) A bat and a ball cost $1.10 in total. The bat costs $1 more than the ball. How much does the ball cost?For answers, and to find out what it means about your valuation of risk, see this Virginia Postrel article.
2) If it takes five machines five minutes to make five widgets, how long would it take 100 machines to make 100 widgets?
3) In a lake, there is a patch of lily pads. Every day, the patch doubles in size. If it takes 48 days for the patch to cover the entire lake, how long would it take for the patch to cover half the lake?
Of particular interest to me is the fact that the better one scores on an extended version of the above quiz, the more likely one is to take a certain form of bad bet, in this example taking a 1% shot of $5000 over a guaranteed $60. I wonder about the theory as to why people who do 'know better' would take that bet. I think I would, even though I'm well aware that it's "-EV". Though of course the result likely gets turned on its head and you invert the problem and offer someone a 1/100 lotto ticket which pays $5000 for a price of $60. I wouldn't do that, (my one night of drunken pull-tab excess aside)