For any base $n$, for $n > 2$ the following holds:
$1/(n-1) = 0.111...$
However in base 2 this doesn't hold. It's just 1. It's obvious why that is you have $1/1$, but I always get uneasy with non-0 and non-1 exceptions in an otherwise flawless rule. Is there any way to shed some light on this?
The equation also holds in base $2$. Note that that claim is the same as the $0.9999\ldots=1$ in the world of ten-finger people.