Please excuse me for asking questions like this while knowing essentially nothing about probability, but **I'd really like to find out what the chances are of $X$ odd digits being present in a number consisting of $N$ digits, where $N$ is greater than or equal to $X$**.

It doesn't sound like a really tough problem to solve (sorry if it's actually really hard!), so I would very much really appreciate a very basic, low-level explanation. 

Thank you for your time!