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Below, a two-way table is given for student activities:

\begin{tabular}{|c|c|c|c|c|}
\hline
& Sports & Drama & Work & Total \\
\hline
Sophomore & 20 & 7 & 3 & 30 \\
\hline
Junior & 20 & 13 & 2 & 35 \\
\hline
Senior & 25 & 5 & 5 & 35 \\
\hline
Total & 65 & 25 & 10 & 100 \\
\hline
\end{tabular}

1. Find the probability that a student is in sports, given that they are a senior.

2. Next, find the probability that a senior is in sports.

[tex]\[ P(\text{senior}) = 0.35 \][/tex]

[tex]\[ P(\text{senior and sports}) = \square \][/tex]

Sagot :

To solve this question, we break it down into two parts as specified:

### Part 1: Determine the Probability a Student is in Sports Given That They Are a Senior
This requires us to determine [tex]\( P(\text{Sports} \mid \text{Senior}) \)[/tex].

From the two-way table, observe the following:
- The total number of seniors is 35.
- The total number of seniors who are in sports is 25.

We apply the conditional probability formula:
[tex]\[ P(\text{Sports} \mid \text{Senior}) = \frac{\text{Number of seniors in sports}}{\text{Total number of seniors}} \][/tex]

By using the numbers directly from the table:
[tex]\[ P(\text{Sports} \mid \text{Senior}) = \frac{25}{35} \][/tex]

In simple mathematical terms:
[tex]\[ P(\text{Sports} \mid \text{Senior}) = \frac{25}{35} = \frac{5}{7} \approx 0.714 \][/tex]

### Part 2: Determine the Probability That It's a Senior and in Sports
This requires us to determine [tex]\( P(\text{Senior and Sports}) \)[/tex].

From the provided data:
- The total number of students is 100.
- The number of seniors who are in sports is 25.

We apply the probability formula for combined events:
[tex]\[ P(\text{Senior and Sports}) = \frac{\text{Number of seniors in sports}}{\text{Total number of students}} \][/tex]

By using the numbers directly from the table:
[tex]\[ P(\text{Senior and Sports}) = \frac{25}{100} \][/tex]

Therefore:
[tex]\[ P(\text{Senior and Sports}) = \frac{25}{100} = \frac{1}{4} = 0.25 \][/tex]

### Summary of Results

1. The probability a student is in sports, given that they are a senior [tex]\( P(\text{Sports} \mid \text{Senior}) \)[/tex] is approximately 0.714.
2. The probability that it’s a senior in sports [tex]\( P(\text{Senior and Sports}) \)[/tex] is 0.25.

So, specifically for the given question:

[tex]\[ P(\text{Senior}) = 0.35 \][/tex]
[tex]\[ P(\text{Senior and Sports}) = 0.25 \][/tex]

These are the detailed solutions for the given probabilities.