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A test was given to a group of students. The grades and gender are summarized below:

[tex]\[
\begin{tabular}{|r|r|r|r|r|}
\hline & A & B & C & Total \\
\hline Male & 16 & 7 & 9 & 32 \\
\hline Female & 18 & 8 & 14 & 40 \\
\hline Total & 34 & 15 & 23 & 72 \\
\hline
\end{tabular}
\][/tex]

Find each of the given probabilities as a reduced fraction.

1. What is the probability that the student was male, given they got a 'B'?

[tex]\[ P(\text{male} \mid B) = \square \][/tex]

2. What is the probability that the student got a 'B', given they are male?

[tex]\[ P(B \mid \text{male}) = \square \][/tex]


Sagot :

Let's solve the given probabilities step-by-step.

### 1. Probability that the student was male given that they got a 'B':

We need to find [tex]\( P(\text{male} \mid B) \)[/tex].

From the given table:
- Number of males who got a 'B': 7
- Total number of students who got a 'B': 15

The formula to calculate [tex]\( P(\text{male} \mid B) \)[/tex] is:
[tex]\[ P(\text{male} \mid B) = \frac{P(\text{male and B})}{P(B)} \][/tex]

Here:
- [tex]\( P(\text{male and B}) \)[/tex] is the probability that a student is both male and got a 'B'. This can be found by the ratio of the number of males who got a 'B' to the total number of students, which is [tex]\( \frac{7}{72} \)[/tex].
- [tex]\( P(B) \)[/tex] is the probability that a student got a 'B'. This can be found by the ratio of the total number of students who got a 'B' to the total number of students, which is [tex]\( \frac{15}{72} \)[/tex].

Now, the probability:
[tex]\[ P(\text{male} \mid B) = \frac{\frac{7}{72}}{\frac{15}{72}} = \frac{7}{15} \][/tex]

### 2. Probability that the student got a 'B' given that they are male:

We need to find [tex]\( P(B \mid \text{male}) \)[/tex].

From the given table:
- Number of students who got a 'B' who are male: 7
- Total number of males: 32

The formula to calculate [tex]\( P(B \mid \text{male}) \)[/tex] is:
[tex]\[ P(B \mid \text{male}) = \frac{P(\text{male and B})}{P(\text{male})} \][/tex]

Here:
- [tex]\( P(\text{male and B}) \)[/tex] is again the probability that a student is both male and got a 'B', which is [tex]\( \frac{7}{72} \)[/tex].
- [tex]\( P(\text{male}) \)[/tex] is the probability that a student is male. This can be found by the ratio of the total number of males to the total number of students, which is [tex]\( \frac{32}{72} \)[/tex].

Now, the probability:
[tex]\[ P(B \mid \text{male}) = \frac{\frac{7}{72}}{\frac{32}{72}} = \frac{7}{32} \][/tex]

Thus, the required probabilities in their reduced fraction forms are:
[tex]\[ P(\text{male} \mid B) = \frac{7}{15} \][/tex]
[tex]\[ P(B \mid \text{male}) = \frac{7}{32} \][/tex]