Question

Suppose that 10% of the undergraduates at a certain university are foreign students, and that 25% of the graduate students are foreign. If there are four times as many undergraduates as graduate students, given that a randomly selected student is foreign, what is the probability that the student is an undergraduate

Answer 1

Answer:

0.6154 = 61.54% probability that the student is an undergraduate

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: Foreign

Event B: Undergraduate.

There are four times as many undergraduates as graduate students

So 4/5 = 80% are undergraduate students and 1/5 = 20% are graduate students.

Probability the student is foreign:

10% of 80%

25% of 20%. So

$P(A) = 0.1*0.8 + 0.25*0.2 = 0.13$

Probability that a student is foreign and undergraduate:

10% of 80%. So

$P(A \cap B) = 0.1*0.8 = 0.08$

What is the probability that the student is an undergraduate?

$P(B|A) = \frac{P(A \cap B)}{P(A)} = \frac{0.08}{0.13} = 0.6154$

0.6154 = 61.54% probability that the student is an undergraduate