You can see quite clearly what setting the group has on the right hand side where they say "about the group" or whatever it is...should say somewhere "this is a xyz group"
If it's a public group then all the posts will be visible to everyone, including all your friends so as CM said it depends on the settings of the group rather than your own settings..If the group is closed then only other members can see posts and if the group is secret no-one outside of the group can see anything, not even the group i!! lol
I think it depends on what type of privacy setting the group admin has set for the page rather than your personal page settings.
Maybe this helps
https://www.facebook.com/help/220336891328465
I've joined a group on FB but it appears that all my details and posts are visible. I've changed my privacy settings to friends only, before joining but it appears that mall my posts are visible - any idea on how to limit access to my profile, I've nothing to hide but prefer to keep my posts accessible to my friends only
Thought by joining a group or liking or following didn't mean all my post were available for all to see.
Thanks in advance