Question

Use the following information for the next two problems. A survey of a group of students reveals that 45% use Facebook, 40% use MySpace, and that 5% use both.

What is the probability that a randomly selected student uses Facebook or MySpace or both?

	a.	0.67
	b.	0.90
	c.	0.85
	d.	0.80

Suppose that a student is selected at random and it’s learned that he/she uses Facebook. Given that, what is the chance that they use MySpace?

	a.	0.050
	b.	0.125
	c.	0.889
	d.	0.111

Answer 1

Let F denotes that the student uses Facebook and M denotes that the student uses MySpace.

Given: P(F) = 0.45, P(M) = 0.40 and P(F M) = 0.05.

Where P(F M) is the probability that the student uses both Facebook and MySpace.

1) The probability that a randomly selected student uses Facebook or MySpace or both is calculated as:

Hence, Option (d) is correct.

2) The probability that a student uses MySpace given that he/she uses Facebook is calculated as:

Hence, Option (d) is correct.