Playing golf with clients is one way to 'mix business with pleasure'. [=to do something enjoyable that is related to your work]
I accidentally 'mixed up' the two files. [=I put each of the files in the place where the other one should have gone]
He 'got mixed up in' a plan to destroy the government. [=he became involved in a plan to destroy the government]
(..) this years cropful troops? Are there any surprises that we can expect this year? It's really hard to tell from a Reaping but I think... ...this is a very interesting mix. Yes. Whenever you have a volunteer from an outline district, it's something you can't ignore. What's that? (..)2012 The Hunger Games