# Thread: Probability: 10 true/false questions, probability at least 7 are correct

1. ## Probability: 10 true/false questions, probability at least 7 are correct

An instructor gives a quiz involving 10 true-questions. To test the hypothesis that he student is guessing, the following rule is adopted:

a) If 7 or more are correct, then the student is not guessing
b) If under 7 is correct, then the student is guessing

Find the probability that the student is not guessing.

So what I was thinking was that you would essentially just make a list of all possible combinations and just find how many have 7 correct questions.. then I realized that certain answers can be true or false and they would still be right (At the time I was thinking of something like 'probability of 7 trues' which is wrong)

After I realized that, I'm stumped. Is there a formula I'm completely forgetting?

2. ## Re: Probability: 10 true/false questions, probability at least 7 are correct

You could think binomial, but I think that would be a bad test for this purpose!

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