Select the correct answer.

The probability of event [tex]\( A \)[/tex] is [tex]\( x \)[/tex], and the probability of event [tex]\( B \)[/tex] is [tex]\( y \)[/tex]. If the two events are independent, which condition must be true?

A. [tex]\( P(B \mid A) = xy \)[/tex]
B. [tex]\( P(B \mid A) = x \)[/tex]
C. [tex]\( P(A \mid B) = x \)[/tex]
D. [tex]\( P(A \mid B) = y \)[/tex]



Answer :

To solve this problem, we first need to recall what it means for two events to be independent. Two events [tex]\(A\)[/tex] and [tex]\(B\)[/tex] are independent if the occurrence of one event does not affect the probability of the occurrence of the other event. Mathematically, this can be defined as:

[tex]\[ P(A \text{ and } B) = P(A) \cdot P(B) \][/tex]

Given that we have two independent events, [tex]\(A\)[/tex] and [tex]\(B\)[/tex], with probabilities [tex]\(P(A) = x\)[/tex] and [tex]\(P(B) = y\)[/tex], we need to determine which of the given statements is true.

Let's inspect each of the given options:

### Option A: [tex]\( P(B \mid A) = xy \)[/tex]

The conditional probability [tex]\( P(B \mid A) \)[/tex] is defined as the probability of [tex]\(B\)[/tex] occurring given that [tex]\(A\)[/tex] has occurred. Using the definition of conditional probability:

[tex]\[ P(B \mid A) = \frac{P(A \text{ and } B)}{P(A)} \][/tex]

Since [tex]\(A\)[/tex] and [tex]\(B\)[/tex] are independent events, we can substitute [tex]\( P(A \text{ and } B) \)[/tex] with [tex]\( P(A) \cdot P(B) \)[/tex]:

[tex]\[ P(B \mid A) = \frac{P(A) \cdot P(B)}{P(A)} = \frac{x \cdot y}{x} \][/tex]

Since [tex]\( x \neq 0 \)[/tex],

[tex]\[ P(B \mid A) = y \][/tex]

This shows that option A, which states [tex]\( P(B \mid A) = xy \)[/tex], is incorrect.

### Option B: [tex]\( P(B \mid A) = x \)[/tex]

From the calculation above, we have shown that:

[tex]\[ P(B \mid A) = y \][/tex]

Thus, option B, which states [tex]\( P(B \mid A) = x \)[/tex], is incorrect.

### Option C: [tex]\( P(A \mid B) = x \)[/tex]

Similarly, the conditional probability [tex]\( P(A \mid B) \)[/tex] is given by:

[tex]\[ P(A \mid B) = \frac{P(A \text{ and } B)}{P(B)} \][/tex]

Using the independence of [tex]\(A\)[/tex] and [tex]\(B\)[/tex],

[tex]\[ P(A \mid B) = \frac{P(A) \cdot P(B)}{P(B)} = \frac{x \cdot y}{y} \][/tex]

Since [tex]\( y \neq 0 \)[/tex],

[tex]\[ P(A \mid B) = x \][/tex]

This shows that option C, [tex]\( P(A \mid B) = x \)[/tex], is correct.

### Option D: [tex]\( P(A \mid B) = y \)[/tex]

From our previous calculation,

[tex]\[ P(A \mid B) = x \][/tex]

So, option D, which states [tex]\( P(A \mid B) = y \)[/tex], is incorrect.

Therefore, the correct answer is:

[tex]\[ \boxed{1} \][/tex]

So, among the given options, the condition that must be true for independent events is represented by option C: [tex]\( P(A \mid B) = x \)[/tex].