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Provide Solution For  R.D.Sharma Maths Class 12 Chapter 30 Probaility  Exercise 30.5 Question 16 Maths Textbook Solution.

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Answer:\frac{107}{120}

Hint: You must know the rules of finding probability.

Given:  A speaks truth three times out of four

B speaks truth four times out of five

C speaks truth five times out of six

Solution:P\left ( A\: Speaks\: truth \right )=\frac{3}{4}

P\left ( B\: Speaks\: truth \right )=\frac{4}{5}

P\left ( C\: Speaks\: truth \right )=\frac{5}{6}

\begin{aligned} &P \text { (majority speaks truth) }=P \text { (two speak truth) }+P(\text { all speak truth }) \\ \end{aligned}

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

\begin{aligned} &=\frac{3}{4} \times \frac{4}{5}\left(1-\frac{5}{6}\right)+\frac{3}{4} \times \frac{5}{6}\left(1-\frac{4}{5}\right)+\frac{4}{5} \times \frac{5}{6}\left(1-\frac{3}{4}\right)+\frac{3}{4} \times \frac{4}{5} \times \frac{5}{6} \\ &=\frac{12}{120}+\frac{15}{120}+\frac{20}{120}+\frac{60}{120} \\ &=\frac{107}{120} \end{aligned}

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