what's the probability that the students get at least 50 on the exam

Question

A student is taking a multiple choice exam that consists of 20 questions and each question has 4 different choices. The student randomly guesses on each question. What is the probability that the student gets at least a 50 on the exam?  Give your answer to four decimal points.

Answer 1

This presumably is a binomial probability question with n = 20, p = 1/4 and q = 3/4.

The required probability is the sum of terms ₂₀C_k * (1/4)^k * (3/4)^20-k for k = 10 to 20.