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Need Solution for R.D.Sharma Maths Class 12 Chapter 30 Probability  Exercise 30.4 Question 19 Maths Textbook Solution.

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Answer:  i. \frac{52}{77}     ii. \frac{25}{77}

Hint: \begin{aligned} P(A \cup B) &=P(A)+P(B)-P(A \cap B) \\ \end{aligned}

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

Given: The odds against event A are 5 to 2. The odds in flavor of event B are 6 to 5.

Solution: As we know, Two events are said to be independent if the product of the events are equal to their intersection. i.e.\begin{aligned} P(A \cap B) &=P(A)P(B)\end{aligned}

The odds against event A are 5 to 2.

                P(A)=\frac{\text { no.of outcome }}{\text { total outcome }}=\frac{2}{5+2}=\frac{2}{7}

The odds in flavor of event B are 6 to 5

                    P(B)=\frac{\text { no.of outcome }}{\text { total outcome }}=\frac{6}{6+5}=\frac{6}{11}         

  1. Probability of atleast one of the event occurs\Rightarrow

            \begin{aligned} P(A \cup B) &=P(A)+P(B)-P(A \cap B) \\ &=\frac{2}{7}+\frac{6}{11}-\frac{2}{7} \times \frac{6}{11} \\ &=\frac{22+42-12}{77} \\ &=\frac{52}{77} \end{aligned}

     ii   P(none of the event occurred) =1-P\left ( A\cup B \right )

                                                                    =1-\frac{52}{77}

                                                                    =\frac{25}{77}

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