At least one is the oppsite of none:
What is the probability that a student will answer at least two questions correctly by random guessing on an exam with 8 multiple-choice questions each of which as three options?
What I don't get is the at least two questions correctly part. Do they mean P(2) + P(3) + P(4) +P(5) + P(6) + P(7) + (P8)?
P(2) means 8C2 x (1/3)^2(2/3)^6 and ect....
That's the answer I got!The answer I came up with is 0.804907788.
Can anybody confirm that I did it correctly?
I did it by using the "opposite" approach.
The opposite of "at least two" is "less than two" (zero or one).
. . Hence: .