Question

A student takes true or false test consisting of 10 questions by just guessing at each answer. Find the probability that the student's score will be 80% or more?

Answer 1

find the prob that he/she will get 8 out of 10, 9 out of 10, or 10 out of 10 correct

I will do the 8 out of 10, you do the others

prob(exactly 8 out of 10)
= C(10,8) (1/2)^8 (1/2)^2
= 45 (1/2)^10
= 45/1024
= appr .0439

Find the other two, and add them up