## Monday, August 29, 2016

### It's Your Birthday! Math trick

A friend of mine shared this math trick with me in my first year of teaching (27 years ago!) The kids love it. I stopped celebrating my students' birthdays in class a few years ago, and at the time it was actually a bit of a relief. It takes time to write down their birthdays and to prepare this little riddle with a piece of candy daily...but I do love it when someone notices my birthday (October 7, cough, cough), so I figured it was worth it for me to put in the extra time to make my students' special day. So this year, I'm back to it. Happily.

Here is a link to the actual picture, above, on plain white paper. I apologize that it's a pdf, but I may have made it up on MS DOS a million years ago, lol. I give it to the birthday student at the beginning of class with a Tootsiepop or some other piece of candy and a silly happy birthday sticker. I have heard of some teachers who make crowns for students to wear (what do you do when there is more than one student who shares the same birthday?) I may go there someday.

When two students have the same birthday, I point it out, as it's a great lead-in to the birthday paradox, which says that in a room of just 23 people, there's a 50% chance of two people having the same birthday. It's also a perfect lead-in to the definition of a function, where two people can have the same birthday (is a function), but one person cannot have two birthdays (not a function). I've taught this method forever, and it's nice for them to see the visual on the board rather than calling on students for their birthdays (which can take forever). Here is a nice powerpoint I found online that demonstrates this. Hannah also talked about this here at TMC16.

It's fun when the student get's their birth date after completing the puzzle and is super excited. Often (unfortunately!), the student makes a math error and then wonders what the heck the answer means! And then I tell them to do it over again. Tenacity is also important to teach!

I just spent an hour putting all my students' birthdays in my planner, and I just wrote August birthdays on a marker board in my class. I will print out all the birthday sheets to hand out for August (most birthdays in August already occurred) and will get my candy ready. It's time-consuming, but if it makes them happy, why wouldn't I do it?