Question

On a recent holiday evening, a sample of 500 drivers was stopped by the police. Three hundred seventy-five were under 30 years of age. A total of 275 were under the influence of alcohol. Of the drivers under 30 years of age, 225 were under the influence of alcohol.
Let A be the event that a driver is under the influence of alcohol.
Let Y be the event that a driver is less than 30 years old.
1. Show the joint probability table.
2. Are A and Y mutually exclusive events? Explain.
3. Are A and Y independent events? Explain.

Answer 1

Answer:

Joint probability table :

_____ A _____ A'

_ Y_ 0.45 ___ 0.30

_ Y'_ 0.05___ 0.20

No

No

Step-by-step explanation:

Given :

Sample, size n = 500

A = driver is under the influence of alcohol :

Y = driver is less than 30 years old

P(A) = 275 / 500 = 0.55

P(Y) = 375 / 500 = 0.75

P(AnY) = 225 / 500 = 0.45

P(YnA') = (1 - 225/375)*0.75 = 0.4 * 0.75 = 0.30

Joint probability table :

_____ A _____ A'

_ Y_ 0.45 ___ 0.30

_ Y'_ 0.05___ 0.20

To determine if it is mutually exclusive : P(AnY) = 0

P(AnY) = 0.45 ; hence, it is not mutually exclusive

For A and Y to be independent ; P(A|Y) = P(A) ;

P(A|Y) = P(AnY) / P(Y)

P(A|Y) = 0.45 / 0.75 = 0.6

Hence, A and Y are not independent.