A little bit of maths

31 12 2013

Last week it was my Dad’s birthday, and he turned the age of the year my Mum was born. We then realised that Mum was the age of the year Dad was born in. I thought a bit further and realised that when my Dad is the age of the year I was born in, then I’ll be the age of the year he was born in. It looked like this worked every time, but it seemed a good opportunity to work out why.

So I thought I’d de rust my brain and see if I could still do a mathsy proof – turned out it was ridiculously straight forward 🙂

define x=(year person a was born) mod 100
define y=(year person b was born) mod 100

person a reaches the age person b was born at year (x+y) mod 100
person b reaches the age person a was born at year (y+x) mod 100

we know x+y=y+x (e.g. call this z), so this will always happen at the same year

QED