When You’ll Ever Use Math

A bachelor party on Catalina Island.

We spent the weekend under a system of penalties and proposition bets. It cost you a dollar if you inadvertently said your wife or girlfriend’s name, for instance, while everyone paid you a dollar for a hole-in-one on the mini-golf course.

Then there were the proposition bets you set up on the side of that system.

“I have a number written down on my hand,” I said during some downtime. “It’s between 0 and 10. I’ll pay out 11:1 to anybody who can guess it. Who wants that action?”

Zac took me on for a dollar and guessed 5. I took his money.

I'm Dan and this is my blog. I'm a former high school math teacher and current head of teaching at Desmos. He / him. More here.


  1. Dan,
    I enjoyed this post! As much for what you didn’t say as what you did. I look forward to seeing you in Kingston (Ontario) this coming May.

  2. They really should have known that you were going to take the money on that one. I love that the 11:1 actually is part of setting the trap, whereas if you had given them even better odds (like 20:1), they might would been tipped off.

  3. Sometimes it’s not about when you’ll use it; it’s about being ready for when someone will try to use it against you. ;)

    Betting against a math teacher who wrote the rules of the bet? I’m picture Zac as just a nice guy who knew he was about to give you a dollar.

  4. Would give them the dollar back if they complained about using a different set of axioms than you?

  5. I think you could have gotten away with at least 15:1, because most people would assume you know some psychological trick at picking a number that most people wouldn’t pick.

  6. The 11:1 odds was intended to suggest the house was at a slight disadvantage, to persuade one that they had an opportunity for a guaranteed 10% return on their wager by covering the spread.

    It relies on a trick though; it exploits the assumption that we have encountered similar situations before and share a common understanding of the problem’s domain. It’s also a language trick; we use the term “number” and “numeral” interchangeably which gives us confidence. Perhaps his point would have been better made had he written ‘e’ on his palm.

  7. How fun! Reminds me of a bumper sticker I once saw: NOBODY promises you whole numbers. (I say this to my students all the time when they think their non-integral answers must be wrong.)

  8. @Fawn I like that; I’m borrowing that for my class.

    I agree with John, your friends should have known better.

    …but I’m still going to try this with my friends.

  9. Oh …i just tried this with my 3rd grade son …and by golly..he blew me with his guess on his second try..

    I had thought of 2.5 as my number and he got it. He could have lucked out but what excited me the most was that he gave me non-whole number as a possible answer. I don’t think I would have gotten it even with my 10th try. :-)

    I am poorer by a few dollars but am glad that the money is still in the family! :-)

    This was a fun exercise. Can’t wait to try it with my husband who we consider the math geek in our family.