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Giving a test to a group of students, the grades and genders are summarized below.

\begin{tabular}{|r|r|r|r|r|}
\hline & A & B & C & Total \\
\hline Male & 14 & 15 & 18 & 47 \\
\hline Female & 17 & 3 & 4 & 24 \\
\hline Total & 31 & 18 & 22 & 71 \\
\hline
\end{tabular}

If one student is chosen at random, find the probability that the student was male OR received a grade of "A". (Leave the answer to four decimal places.)


Sagot :

To solve this problem, we can proceed step-by-step to find the probability that a randomly chosen student is either male or received a grade of "A". This involves calculating several intermediate probabilities and then combining them using the principle of inclusion-exclusion.

Here is the detailed solution:

1. Total Number of Students:
The total number of students is the sum of all male and female students:
[tex]\[ \text{Total Students} = 47 + 24 = 71 \][/tex]

2. Total Number of Males:
According to the table, the total number of male students is:
[tex]\[ \text{Total Males} = 47 \][/tex]

3. Total Number of Students who Received an "A":
The students who received an "A" include both males and females who received an "A":
[tex]\[ \text{Total A} = 14 (\text{Males who received an A}) + 17 (\text{Females who received an A}) = 31 \][/tex]

4. Number of Male Students who Received an "A":
We already have this information from the table:
[tex]\[ \text{Male A} = 14 \][/tex]

5. Calculate the Probability of Selecting a Male or a Student who Received an "A":
Using the principle of inclusion-exclusion for probability:
[tex]\[ P(\text{Male OR A}) = P(\text{Male}) + P(\text{A}) - P(\text{Male AND A}) \][/tex]
Where:
[tex]\[ P(\text{Male}) = \frac{\text{Total Males}}{\text{Total Students}} = \frac{47}{71} \][/tex]
[tex]\[ P(\text{A}) = \frac{\text{Total A}}{\text{Total Students}} = \frac{31}{71} \][/tex]
[tex]\[ P(\text{Male AND A}) = \frac{\text{Male A}}{\text{Total Students}} = \frac{14}{71} \][/tex]

6. Substitute the Values into the Formula:
[tex]\[ P(\text{Male OR A}) = \frac{47}{71} + \frac{31}{71} - \frac{14}{71} \][/tex]
[tex]\[ P(\text{Male OR A}) = \frac{47 + 31 - 14}{71} = \frac{64}{71} \][/tex]

7. Convert the Fraction to a Decimal:
[tex]\[ P(\text{Male OR A}) \approx 0.9014 \][/tex]

Therefore, the probability that a randomly chosen student is either male or received a grade of "A" is [tex]\(0.9014\)[/tex] when rounded to four decimal places.