Question

An examination consists of multiple-choice questions, each having five possible answers. Linda estimates that she has probability 0.4 of knowing the answer to any question that may be asked. If she does not know the answer, she will guess, with conditional probability 1/5 of being correct.A. What is the probability that Linda gives the correct answer to a question? B. What is the conditional probability that Linda knows the answer, given that she supplies the correct answer?

Answer 1

Answer:

a. 0.52 = 52% probability that Linda gives the correct answer to a question.

b. 0.7692 = 76.92% probability that Linda knows the answer

Step-by-step explanation:

Conditional Probability

We use the conditional probability formula to solve this question. It is

$P(B|A) = \frac{P(A \cap B)}{P(A)}$

In which

P(B|A) is the probability of event B happening, given that A happened.

$P(A \cap B)$ is the probability of both A and B happening.

P(A) is the probability of A happening.

In this question:

Event A: Supplies the correct answer:

Event B: Knows the answer

A. What is the probability that Linda gives the correct answer to a question?

0.4(knows the answer)

1/5 = 0.2 of 1 - 0.4 = 0.6(guesses the answer). So

$P(A) = 0.4 + 0.2*0.6 = 0.52$

0.52 = 52% probability that Linda gives the correct answer to a question.

B. What is the conditional probability that Linda knows the answer, given that she supplies the correct answer?

Intersection of events A and B is knowing the answer and giving the correct answer, which means that $P(A \cap B) = 0.4$

The desired probability is:

$P(B|A) = \frac{P(A \cap B)}{P(A)} = \frac{0.4}{0.52} = 0.7692$

0.7692 = 76.92% probability that Linda knows the answer