Events mathrm{A} and mathrm{B} are such that mathrm{P}(mathrm{A})=frac{1}{2}, mathrm{P}(mathrm{B})=f

English

Gujarati

Hindi

14.Probability

medium

Events $\mathrm{A}$ and $\mathrm{B}$ are such that $\mathrm{P}(\mathrm{A})=\frac{1}{2}, \mathrm{P}(\mathrm{B})=\frac{7}{12}$ and $\mathrm{P}$ $($ not $ \mathrm{A}$ or not $\mathrm{B})=\frac{1}{4} .$ State whether $\mathrm{A}$ and $\mathrm{B}$ are independent?

Option A

Option B

Option C

Option D

Solution

It is given that $\mathrm{P}(\mathrm{A})=\frac{1}{2}, \mathrm{P}(\mathrm{B})=\frac{7}{12} \text { and } \mathrm{P}(\text { not } \mathrm{A} \text { or not } \mathrm{B})=\frac{1}{4}$.

$\Rightarrow \mathrm{P}\left(\mathrm{A}^{\prime} \cup \mathrm{B}^{\prime}\right)=\frac{1}{4}$

$\Rightarrow P\left((A \cap B)^{\prime}\right)=\frac{1}{4} \quad\left[A^{\prime} \cup B^{\prime}=(A \cap B)^{\prime}\right]$

$\Rightarrow 1-\mathrm{P}(\mathrm{A} \cap \mathrm{B})=\frac{1}{4}$

$\Rightarrow \mathrm{P}(\mathrm{A} \cap \mathrm{B})=\frac{3}{4}$ ……….. $(1)$

However, $\mathrm{P}(\mathrm{A}) \mathrm{P}(\mathrm{B})=\frac{1}{2} \cdot \frac{7}{12}=\frac{7}{24} $ ………. $(2)$

Here, $\frac{3}{4} \neq \frac{7}{24}$

$\therefore $ $\mathrm{P}(\mathrm{A} \cap \mathrm{B}) \neq \mathrm{P}(\mathrm{A}) \mathrm{P}(\mathrm{B})$

Therefore, $A$ and $B$ are not independent events.

Standard 11

Mathematics

One bag contains $5$ white and $4$ black balls. Another bag contains $7$ white and $9$ black balls. A ball is transferred from the first bag to the second and then a ball is drawn from second. The probability that the ball is white, is

hard

If $A$ and $B$ are two independent events such that $P\,(A) = 0.40,\,\,P\,(B) = 0.50.$ Find $P$ (neither $A$ nor $B$)

easy

If $P(A) = 0.25,\,\,P(B) = 0.50$ and $P(A \cap B) = 0.14,$ then $P(A \cap \bar B)$ is equal to

easy

Urn $A$ contains $6$ red and $4$ black balls and urn $B$ contains $4$ red and $6$ black balls. One ball is drawn at random from urn $A$ and placed in urn $B$. Then one ball is drawn at random from urn $B$ and placed in urn $A$. If one ball is now drawn at random from urn $A$, the probability that it is found to be red, is

hard

(IIT-1988)

Two cards are drawn at random and without replacement from a pack of $52$ playing cards. Finds the probability that both the cards are black.