how do you find the probability of how many answers you will get correct on a test?

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Suppose that a multiple choice quiz has 10 questions each with 5 possible choices. Find the probability of guessing 2 questions correct.

would the answer be .00671
 
You can use a binomial distribution.
p = 1/5 (get it right)
q = 4/5 (get it wrong)

You want the probability you get 2 right (and 8 wrong).
P(k = 2) = C(10,2) p^2 q^8
= (10 x 9) / 2 * (1/5)^2 (4/5)^8
= 0.301989888

Answer:
≈ 30.2%

P.S. You computed the probability of getting 2 *specific* problems correct and the other 8 wrong (say the first two right, the last 8 wrong). But you need to multiply by the number of ways to have 2 correct answers anywhere on the test. That is C(10,2) = 45. So multiply your answer by 45.
 
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