OK- there are different types of probability formulas, depending on what you want to look at. There is not enough info in your OP to determine your needs. Plus, you're going to have to determine your confidence interval, a power analysis might be in order to determine how many participants you need, etc.
You shouldn't have to include your actual analysis in a research proposal, anyway. The proposal is submitted before you even begin collecting and analyzing data. You should include what methods you plan to use etc., but not your analysis.
I would suggest speaking with your instructor about this for guidance. S/he will be able to tell you what to do if you have your proposal there in front of you. From the OP it isn't even clear why you're using probability, and you may need to use something more appropriate, or with more statistical strength instead.
Good luck to you.