I posted this in another thread but thought i would make a new one anyways.

Take the last two digits of the year that you were born and add it to the age that you will be THIS year and it should equal 111.

It will work as long as you were born between 1900 and 1999.

BUT WHY?!

sister came up with 110

Were you born after 1999?

GREAT SCOTT!!! I think you've foiled sisters plans to perform dastardly deeds.

f(X) = (2011-X)+(X-1900) = 111 for any whole number X (the year you were born).
next year, the number will change to 112...

i see! Thanks alzabo! So Dr_Sister might have accidentally put in the wrong age or year to get 110?

Perhaps she hasn't had her birthday yet this year. I got 110 as well 'till I realized that I was supposed to put one number higher for my age.
The funny thing is that this function still gives 111 even for negative numbers.

In a bit more detail, (2011-X) + (X-1900) = 2011 - 1900 + X - X = 2011 - 1900 = 111

I thought that too. You have to put in the age you are GOING to turn this year and if you already had your b-day you just put in the age you are.

That's weird about the negative numbers. I like it!