[R] OT: Statistics question

[tom wright]

I apologise for asking this question here but I am hoping that someone
can either give me direct guidance and/or point me to a better group for
this type of disucssion.

I have what I feel should be a fairly simple problem but which my
limited stats knowledge can't answer. I have two overlapping
distributions (both normal) and I want to answer the question how do I
calculate the cut-off value so I can be 95% sure that samples => than
the cut off fall in the right hand distribution?

A while ago I did a bayesian statistics course that I think answered
this very question but in the absence of any course notes or recent
practice Ihave forgotten how to go about this.

Many thanks for your time
Tom