Question

A multiple-choice test consists of 10 questions. Each question has answer choices of a ,b c, d ,e , and , and only one of the choices is correct. If a student randomly guesses on each question, what is the probability that he gets at least 2 of them correct?

Answer 1

Its easier to find the complement of that instead
so you find the probability of 1 and 0
The .2 in the answer is the probability of each question 1/5
  (10 C 0) x .2^0 (1-.2)^10-0=.1074
 (10 C 1) x .2^1 (1-.2)^10-1=.2684
.2684+.1074=.3758 and that's the complement
so 1 - .3758= .6242
I too have a stats exam on this tomorrow lol