please help!
if given multiple choice test with 10 questions and each having 5 choices, what is the prob of getting atleast one correct? also of getting no more than two correct?

jt,

This is a binomial situation - it is assumed that the person is guessing at the answers, and the outcome on each question is either "right" or "wrong." The probabilities of getting a certain number of questions correct (0 to 10) must add up to 1.

Use the binomial formula, with

p = 0.2 (the probability of guessing correctly on any given question)
q = 1-p = 0.8 (the probability of guessing incorrectly)
n = 10 (total number of questions)

Find the probability of getting 0 correct (set x=0), then subtract this answer from 1 -->that will get you the first answer ("at least 1 correct")

For the second part ("no more than 2") --> set x=0, x=1, x=2 and find the probabilities for each, and then add them up.