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A company insures red and black cars, male and female drivers and writes policies in 2 territories (A and B). There are 300 male drivers and 200 female drivers in total. There are 150 males who drive red cars and 100 females who drive red cars. 100 male and 100 female drivers live in territory A and 50 of each, males and females, drive red cars in territory A. Given that a randomly selected policyholder drives a black car, what is the probability that they are female and live in territory B?
A
20%
B
25%
C
33%
D
40%
Explanation:
We need to find P(Female ∩ Territory B | Black Car) = P(Female, Territory B, Black Car) / P(Black Car)
Step 1: Organize the data
Total drivers:
Red car drivers:
Black car drivers:
Territory A:
Territory B:
Step 2: Fill the contingency table
From the given: "50 of each, males and females, drive red cars in territory A"
So:
Now we can complete the table:
Male drivers (300 total):
Female drivers (200 total):
Step 3: Calculate probabilities
P(Female, Territory B, Black Car) = Number of female black car drivers in territory B / Total drivers = 50 / 500 = 0.10
P(Black Car) = Total black car drivers / Total drivers = 250 / 500 = 0.50
Step 4: Conditional probability
P(Female ∩ Territory B | Black Car) = P(Female, Territory B, Black Car) / P(Black Car) = 0.10 / 0.50 = 0.20 = 20%
Verification with table:
| Territory A | Territory B | Total | ||
|---|---|---|---|---|
| Male | Red Car | 50 | 100 | 150 |
| Male | Black Car | 50 | 100 | 150 |
| Female | Red Car | 50 | 50 | 100 |
| Female | Black Car | 50 | 50 | 100 |
| Total | 200 | 300 | 500 |
Total black cars = 150 + 100 = 250 Female black in B = 50 Probability = 50/250 = 0.20 = 20%
Therefore, the correct answer is 20% (Option A).