Question

Suppose that 1/2 of all cars sold at a Nissan dealer in a given year are Altimas, 1/3 are Maximas, and the rest are Sentras. Suppose that 3/4 of the Altimas, 1/2 of the Maximas, and 1/2 of the Sentras have a moon roof. Answer the following questions. For each question, first decide whether the probability is a conditional probability or not.1. What is the probability a randomly selected car has a moon roof?

2. What is the probability that a randomly selected car has a moon roof given it is a Sentra?
3. What is the probability a randomly selected car is a Maxima if it has a moon roof?

Answer 1

(1) Not conditional, 5/8

(2) Not conditional, 1/12

(3) Conditional, 1/18

Explanation:

Fraction of cars sold

Altima = 1/2

Maxima = 1/3

Sentra = 1 - (1/2 + 1/3) = 1 - 5/6 = (6 - 5)/6 = 1/6

Fraction of cars sold with moon roof

Altima = 3/4 × 1/2 = 3/8

Maxima = 1/2 × 1/3 = 1/6

Sentra = 1/2 × 1/6 = 1/12

(1) Probability (a randomly selected car has a moon roof) = 3/8 + 1/6 + 1/12 = (9+4+2)/24 = 15/24 = 5/8

(2) Probability (a randomly selected car has a moon roof given it is Sentra) = 1/12

(3) Probability (a randomly selected car is a Maxima if it has a moon roof) = 1/3 × 1/6 = 1/18

A conditional probability uses if (as a condition) in making statements or asking questions

An unconditional probability makes statement or ask question without the use of condition (if)