Number Theory: Real Life Math

During the March break, I found my bib number on Boston’s site: 15135, 2nd wave, 7th corral.  I’m at the back, but I still love the number.

When I got back to school after the break, the kids shared their March Break stories and I told them that I received my bib number and challenged them to guess why I liked it so much.

After 3 guesses, one of them said it was my birthdate.  “Yes,” I answered as I drew a box around 15. “I love the number 15, probably because I was born on September 15th.”   Keep going; there are other reasons.

They came up with all sorts of wild reasons. “You were born in 1135″ was my favorite.  When I asked them to think about multiples of 15, more hands went up.”Yes, 135 is a multiple of 15.”

“Wait!” blurted one of the boys.  “When you add the digits in 135, you get 9 and 9 is the ninth month of the year: September.  Didn’t you say you were born on September 15th?”  I didn’t see that one coming at all!

“Okay, now keep thinking multiples.  My goal time is between 3:30 and 3:45, or 210 and 225 minutes.”
I could see the wheels turning as they kept playing with numbers.  Eventually, they realized that 210 and 225 are also multiples of 15, and so are 330 and 345 when written without the colons.

So, 15135 speaks to me.  I can’t wait to put it on!

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