College Finite Math
posted by Taymor on .
Involving a truefalse test. Assume that 8 questions are answered by guessing.
What is the probability of at least 6 correct answers?
I know this a Burnoulli Trial problem and that N=8 and p=.5 and q=.5
I just don't know where to go from there.

Add the probabilities of 6, 7 and 8 correct answers. The probability of getting all 8 right is (1/2)^8 = 1/256
The probability of getting 6 right is (1/2)^8*8!/[6!*2!] = 56/[256*2] = 28/256
The probability of getting 7 right is
(1/2)^8*8!/[7!*1!]= 8/256
The total probability is 37/256