Hey

Im new here, and i'm not sure where to put this Q,

I was studying for the AMO, and I came across a problem in the 2004 AIMO which has me completely stuck ...

A new binary operation ? defined on all positive x and y, satisfies the following conditions:

i x?x = x+2

ii x?y = y?x

iiix?(x+y)=x+y

----x?y------y

Given the above, find 11?8

please explain how to do this, i have been to other forums, and unless I ask, they just give a number.

Thanks