posted by Matt Borchelt .
a 10 question multiple choice test has 4 possible answer for each question. A student selects at least 6 correct answers.
Find probability of this event:
he got 6 right, 4 wrong. The question has no answer. Did he randomly guess, or did he know the answers to only six?
If he knew the answers to six, the probability is 1 that he gets those six.
If he knows 5, the prob is 1 he gets those right, plus pr =4(1/4)(3/4) he gets one more or a pr of .75 he gets six right knowing 5, guessing on the last four.
Well, we need to know how many he knew, I think.