Question

A teacher gave a 3-question multiple choice quiz. Each question had 4 choices to select from. If the a student completely guessed on every problem, what is the probability that they will have 2 or less correct answers?

Answer 1

0.9844

Explanation:

This is a binomial probability problem.

Probability of getting a correct answer: p = 1/4

Probability of getting an incorrect answer: q = 3/4

Number of questions; n = 3

Thus;

probability of 2 or less correct answers is; P(x ≤ 2) = P(X = 2) + P(X = 1) + P(X = 0)

From binomial probability the formula is;

P(X = x) = C(n, x) × p^(x) × q^(n - x)

P(X = 2) = C(3, 2) × (¼)² × (¾)¹

P(X = 2) = 3 × 0.0625 × 0.75

P(X = 2) = 0.1406

P(X = 1) = C(3, 1) × (¼)¹ × (¾)²

P(X = 1) = 3 × 0.25 × 0.5625

P(X = 1) = 0.4219

P(X = 0) = C(3, 0) × (¼)^(0) × (¾)³

P(X = 0) = 0.4219

P(x ≤ 2) = 0.1406 + 0.4219 + 0.4219

P(x ≤ 2) = 0.9844