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The director of health services is concerned about a possible flu outbreak at her college. She surveyed 100 randomly selected residents from the college's dormitories to see whether they had received a preventative flu shot. The results are shown below.

What is the probability that a dormitory resident chosen at random from this group has had a flu shot, given that he is male?

Residents at College Dormitories:

\[
\begin{tabular}{|c|c|c|c|}
\hline
& \text{Male} & \text{Female} & \text{Total} \\
\hline
\text{Had Flu Shot} & 39 & 41 & 80 \\
\hline
\text{Didn't Have Flu Shot} & 12 & 8 & 20 \\
\hline
\text{Total} & 51 & 49 & 100 \\
\hline
\end{tabular}
\]

Calculate the probability.

Answer :

- Define events: $A$ is having a flu shot, $B$ is being male.
- Use conditional probability formula: $P(A|B) = \frac{P(A \cap B)}{P(B)}$.
- Calculate $P(A \cap B) = \frac{39}{100}$ and $P(B) = \frac{51}{100}$.
- Substitute and simplify: $P(A|B) = \frac{39}{51} = \boxed{\frac{13}{17}}$.

### Explanation
1. Understand the problem and provided data
We are given a table that summarizes the results of a survey about flu shots among college dormitory residents. The goal is to find the probability that a randomly chosen dormitory resident has had a flu shot, given that the resident is male.

2. Define events and conditional probability formula
Let $A$ be the event that a resident has had a flu shot, and let $B$ be the event that a resident is male. We want to find the conditional probability $P(A|B)$, which is the probability that a resident has had a flu shot given that the resident is male. The formula for conditional probability is: $$P(A|B) = \frac{P(A \cap B)}{P(B)}$$

3. Calculate $P(A
cap B)$
$P(A \cap B)$ is the probability that a resident is male and has had a flu shot. From the table, there are 39 male residents who had a flu shot out of the 100 total residents. So, $$P(A \cap B) = \frac{39}{100}$$

4. Calculate $P(B)$
$P(B)$ is the probability that a resident is male. From the table, there are 51 male residents out of the 100 total residents. So, $$P(B) = \frac{51}{100}$$

5. Apply the conditional probability formula
Now, we substitute these values into the conditional probability formula:$$P(A|B) = \frac{\frac{39}{100}}{\frac{51}{100}} = \frac{39}{51}$$

6. Simplify and conclude
We simplify the fraction $\frac{39}{51}$ by dividing both the numerator and the denominator by their greatest common divisor, which is 3:$$\frac{39}{51} = \frac{39 \div 3}{51 \div 3} = \frac{13}{17}$$Therefore, the probability that a dormitory resident chosen at random from this group has had a flu shot, given that he is male, is $\frac{13}{17}$.

### Examples
Understanding conditional probabilities is very useful in real life. For example, in medical testing, it helps doctors determine the probability of a patient having a disease given a positive test result, considering the test's accuracy and the prevalence of the disease in the population.

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Rewritten by : Barada