how do I work out the probability of taking two of the same flavour yoghurts from the fridge the second time after eating the first one

I have no idea what you are asking. Can you please re-word it and include all the info that was given in the problem. (i.e. don't try to paraphrase it.)

And also see our guidelines about posting homework in the big red print at the top of the page. See if you can at least make an attempt to do the problem.

Toronto, are there any other types of yoghurt in the fridge of your problem? If no, then you are sure that you'll take the same flavour yoghurt. That is, the probability will be 1.