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For a certain population of employees, the percentage
Chapter 2, Problem 72E(choose chapter or problem)
For a certain population of employees, the percentage passing or failing a job competency exam, listed according to sex, were as shown in the accompanying table. That is, of all the people taking the exam, 24% were in the male-pass category, 16% were in the male-fail category, and so forth. An employee is to be selected randomly from this population. Let A be the event that the employee scores a passing grade on the exam and let M be the event that a male is selected.
\(\begin{array}{lccr}
\hline &{\text { Sex }} & \\
\text { Outcome } & \text { Male }(M) & \text { Female }(F) & \text { Total } \\
\hline \text { Pass }(A) & 24 & 36 & 60 \\
\text { Fail }(\bar{A}) & 16 & 24 & 40 \\
\text { Total } & 40 & 60 & 100 \\
\hline
\end{array}\)
a Are the events A and M independent?
b Are the events \(\bar{A}\) and F independent?
Questions & Answers
(1 Reviews)
QUESTION:
For a certain population of employees, the percentage passing or failing a job competency exam, listed according to sex, were as shown in the accompanying table. That is, of all the people taking the exam, 24% were in the male-pass category, 16% were in the male-fail category, and so forth. An employee is to be selected randomly from this population. Let A be the event that the employee scores a passing grade on the exam and let M be the event that a male is selected.
\(\begin{array}{lccr}
\hline &{\text { Sex }} & \\
\text { Outcome } & \text { Male }(M) & \text { Female }(F) & \text { Total } \\
\hline \text { Pass }(A) & 24 & 36 & 60 \\
\text { Fail }(\bar{A}) & 16 & 24 & 40 \\
\text { Total } & 40 & 60 & 100 \\
\hline
\end{array}\)
a Are the events A and M independent?
b Are the events \(\bar{A}\) and F independent?
ANSWER:Step 1 of 2:
(a)
In this question, we are asked to find whether the events A and M are independent or not.
The percentage passing or failing a job competency exam, listed according to sex, were as shown in the table.
24% were in the male-pass category, 16% were in the male-fail category.
Let A be the event that the employee pass the exam.
Let M be the event that a male is selected.
\(\begin{array}{|l|l|l|l|}
\hline \text { Outcome } & \text { Male }(M) & \text { Female }(F) & \text { Total } \\
\hline \text { Pass }(A) & 24 & 36 & 60 \\
\hline \text { Fail }(\bar{A}) & 16 & 24 & 40 \\
\hline \text { Total } & 40 & 60 & 100 \\
\hline
\end{array}\)
Probability that the employee scores a passing grade on the exam,
\(P(A)=\frac{60}{100}=0.6[\text { from the table }]\)
Probability that the employee fails on the exam,
\(P(\bar{A})=\frac{40}{100}=0.4[\text { from the table }]\)
Hence we need to find the conditional probability that the employee scores a passing grade on the exam, given that the employee is male,
\(P(A \mid M)=\frac{P(A \cap M)}{P(M)} \ldots \ldots \ldots(1)\)
From the table,
\(\begin{array}{l}
P(A \cap M)=\frac{24}{100}=0.24\\
P(M)=\frac{40}{100}=0.4\\
P(A \mid M)=\frac{0.24}{0.4}=0.6 .
\end{array} \dots \dots (2)\)
If the events A and M are independent, then we can write,
\(P(A \cap M)=P(A) \times P(M) \ldots \ldots \ldots(3)\)
Therefore we can rewrite the equation (1) ,
\(\begin{array}{l}
P(A \mid M)=\frac{P(A) \times P(M)}{P(M)}=P(A)\\
P(A \mid M)=P(A)=0.6
\end{array} \dots \dots (4)\)
We can see that the value of equation (2) and (4) are equal, which means both events are independent.
Hence the events A and M are independent.
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