## 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. #### Bill Lundy

March 5, 2012 - 9:59 am -

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.
Bill

2. #### Rob

March 5, 2012 - 10:30 am -

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. #### Dave

March 5, 2012 - 10:36 am -

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. #### Mark Watkins

March 5, 2012 - 11:37 am -

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

5. #### Zach Elwood

March 5, 2012 - 11:46 am -

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. #### corn

March 5, 2012 - 1:30 pm -

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. #### Fawn Nguyen

March 6, 2012 - 7:48 am -

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. #### Matt Vaudrey

March 6, 2012 - 8:05 am -

@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. #### Aruna

March 6, 2012 - 3:59 pm -

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.