Probability, multiple choice

Question

Jean guesses on all 7 questions on her multiple choice quiz. Find the probability if each question has 4 choices.

P(exactly 6 correct)

P(at most 2 correct)

Answer 1

use binomial probability formula:

given probability (p), n trials, probability of x successes =

n!

--- p^x (1-p)^n-x

x! (n-x)!

for the first problem n = 7, x = 6 and p = 1/4 = 0.25.

for the second problem, n = 7 and p = 0.25, you need to find then sum probabilities for x = 0, 1 and 2.