I'm having difficulty solving this question :
In a multiple choice test there are 5 questions each with three possible answers. For each question a student chooses an answer at random. Find the probability that she gets
A) exactly 3 correct answers
B) three or fewer.
This is how i solved A:
$P(X=3)=p(3)= 10(.33^3)(.67^2) = 0.1613$
10 is the number of possibilities to get 3 questions right from 5 questions. I wad wondering if this method is correct and also i have no idea how to apply my current formula to section B.