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Provide solution for RD Sharma Maths Class12 Chapter 30 Probability Exercise Fill in the Blanks Question, Question 1.

Answers (1)

Answer:  P(A)P(\overline{B})

Given:

If A and B are independent events then P(A∪B)=1-x where x=…. -

Hint:

Using P(A)=1-P(A) ; P(A)=1-P(A)

Explanation:

We are given
A and \overline{B} an indepindent events
\Rightarrow \overline{A} and B oure also independent

Since \overline{A} and B are independent events.

\mathrm{P}(\overline{\mathrm{A}} \cap \mathrm{B})=\mathrm{P}(\overline{\mathrm{A}}) \mathrm{P}(\mathrm{B})                                            

Now 

\begin{aligned} &\mathrm{P}(\overline{\mathrm{A}} \cup \mathrm{B})=\mathrm{P}(\overline{\mathrm{A}})+\mathrm{P}(\mathrm{B})-\mathrm{P}(\overline{\mathrm{A}} \cap \mathrm{B}) \\ &=(1-\mathrm{P}(\mathrm{A}))+(1-\mathrm{P}(\overline{\mathrm{B}}))-\mathrm{P}(\overline{\mathrm{A}}) \mathrm{P}(\mathrm{B}) \\ &=(1-\mathrm{P}(\mathrm{A}))+(1-\mathrm{P}(\overline{\mathrm{B}}))-\cdot(1-\mathrm{P}(\mathrm{A}))(1-\mathrm{P}(\overline{\mathrm{B}})) \end{aligned}

\begin{aligned} &=1-\mathrm{P}(\mathrm{A})+1-\mathrm{P}(\overline{\mathrm{B}})-[1-\mathrm{P}(\mathrm{A})-\mathrm{P}(\mathrm{A})+\mathrm{P}(\mathrm{A}) \mathrm{P}(\overline{\mathrm{B}})] \\ &=1-\mathrm{P}(\mathrm{A})+1-\mathrm{P}(\overline{\mathrm{B}})-1+\mathrm{P}(\mathrm{A})+\mathrm{P}(\mathrm{B})-\mathrm{P}(\mathrm{A})(\overline{\mathrm{B}}) \\ &=1-\mathrm{P}(\mathrm{A}) \mathrm{P}(\overline{\mathrm{B}}) \\ &\Rightarrow \mathrm{P}(\overline{\mathrm{A}} \cup \mathrm{B})=1-\mathrm{P}(\mathrm{A}) \mathrm{P}(\overline{\mathrm{B}})-(1) \end{aligned}

Also given that P(\overline{A}\cup B)=1-x-(2)

Comparing (1) and 2 we get x=1-P(A)P(\overline{B})

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