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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? A)51 / 100 B)39 / 100 C)39 / 80 D)13 / 17
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Step 1:
: First, we need to determine how many males in the sample of 100 students have had a flu shot.

The problem states that 39 out of the 51 males surveyed had received a flu shot.

Step 2:
: Now, we need to calculate the probability of choosing a male student who has had a flu shot.

P(\text{Male and Flu Shot}) = \frac{\text{Number of males with flu shot}}{\text{Total number of males}}
To do this, we'll divide the number of males who had a flu shot by the total number of males in the survey. The probability P(Male and Flu Shot) is calculated as:

Step 3:
: Substituting the values from the problem into the formula:

P(\text{Male and Flu Shot}) = \frac{39}{51}

Step 4:
: Now, we need to calculate the probability that a male student is chosen, given that he has had a flu shot.

P(\text{Male | Flu Shot}) = \frac{P(\text{Male and Flu Shot})}{P(\text{Flu Shot})}
This is the conditional probability P(Male | Flu Shot). To find this, we'll divide the probability of choosing a male with a flu shot by the probability of choosing any student with a flu shot.

Step 5:
: We already calculated P(Male and Flu Shot) in Step 3.

P(\text{Flu Shot}) = \frac{\text{Total number of students with flu shot}}{\text{Total number of students surveyed}}
Now, we need to find P(Flu Shot). To do this, we'll divide the total number of students with flu shots by the total number of students surveyed:

Step 6:
: Substituting the values from the problem into the formula:

P(\text{Flu Shot}) = \frac{39 + 12}{100} = \frac{51}{100}

Step 7:
: Now, we can calculate the conditional probability P(Male | Flu Shot):

P(\text{Male | Flu Shot}) = \frac{P(\text{Male and Flu Shot})}{P(\text{Flu Shot})} = \frac{39/51}{51/100} = \frac{39}{51} \times \frac{100}{51} = \frac{13}{17}

Final Answer

The probability that a dormitory resident chosen at random from this group is male, given that he has had a flu shot, is \frac{13}{17}.