edited by
4,130 views
16 votes
16 votes

Consider two events $E_1$ and $E_2$ such that probability of $E_1$, $P_r[E_1]=\frac{1}{2}$, probability of $E_2$, $P_r[E_{2}]=\frac{1}{3}$, and probability of $E_1$, and $E_2$, $P_r[E_1 \: and \: E_2] = \frac{1}{5}$. Which of the following statements is/are true?

  1. $P_r[E_1\: \text{or} \:E_2] \text{ is } \frac{2}{3}$

  2. Events $E_1$ and $E_2$ are independent

  3. Events $E_1$ and $E_2$ are not independent

  4. $P_r \left[{E_1}\mid{E_2} \right] = \frac{4}{5}$

edited by

2 Answers

Best answer
16 votes
16 votes
For $A$:

$P(E_1\cup E_2)=P(E_1)+P(E_2)-P(E_1\cap E_2)$

                         $=\frac{1}{2}+\frac{1}{3}-\frac{1}{5}$

                         $=\frac{19}{30}$ $\neq \frac{2}{3}$    $\therefore$ $A$ is not True

For$B$:

If $E_1$ and $E_2$ are independent then

$P(E_1\cap E_2)=P(E_1)P(E_2)$

                         $=\frac{1}{2}\times\frac{1}{3}$

                         $=\frac{1}{6}$  $\neq \frac{1}{5}$      $\therefore$ $B$ is not True

For $D$:

$P\left ( \frac{E_1}{E_2} \right )=\frac{P(E_1\cap E_2)}{P(E_2)}$

                 $=\frac{\frac{1}{5}}{\frac{1}{3}}=\frac{3}{5} \neq \frac{4}{5}$  $\therefore$ $D$ is not True

So, the answer is $C$, $E_1$ and $E_2$ are not independent
edited by
Answer:

Related questions

37 votes
37 votes
4 answers
1
24 votes
24 votes
2 answers
2
Kathleen asked Oct 4, 2014
4,438 views
Let $A, B,$ and $C$ be independent events which occur with probabilities $0.8, 0.5,$ and $0.3$ respectively. The probability of occurrence of at least one of the event is...
35 votes
35 votes
3 answers
3
6 votes
6 votes
2 answers
4