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Explain Solution R.D. Sharma Class 12 Chapter 30 Probability  Exercise 30.5 Question 35 Maths Textbook Solution.

Answers (1)

Answer: P\left ( Team\: A \right )=\frac{6}{11}

  P\left ( Team\: B \right )=\frac{5}{11}

The decision was fair as the two probabilities are almost equal.

Hint: You must know the rules of finding probability functions.

Given: In a hockey match, both teams scored same number of goals upto end of the game.

Solution:

P\left ( a\: six \right )=\frac{1}{6}

P\left ( not\: a\: six \right )=\frac{5}{6}

\begin{aligned} &P(\mathrm{~A} \text { wins })=P(6 \text { in first throw })+P(6 \text { in third throw })+\ldots \\ \end{aligned}

\begin{aligned} &=\frac{1}{6}+\left(\frac{5}{6} \times \frac{5}{6} \times \frac{1}{6}\right)+\ldots . . \\ &=\frac{1}{6}\left[1+\left(\frac{5}{6}\right)^{2}+\left(\frac{5}{6}\right)^{4}+\ldots\right] \\ \end{aligned}

\begin{aligned} &=\frac{1}{6}\left[\frac{1}{1-\frac{25}{36}}\right] \quad\left[1+a+a^{2}+a^{3}+\ldots=\frac{1}{1-a}\right] \\ &=\frac{1}{6} \times \frac{36}{11} \\ &=\frac{6}{11} \end{aligned}

\begin{aligned} &P(\mathrm{~B} \text { wins })=P(6 \text { in second throw })+P(6 \text { in fourth throw })+\ldots \\ \end{aligned}

\begin{aligned} &=\frac{5}{6} \times \frac{1}{6}+\left(\frac{5}{6} \times \frac{5}{6} \times \frac{5}{6} \times \frac{1}{6}\right)+\ldots . . \\\\ &=\frac{5}{36}\left[1+\left(\frac{5}{6}\right)^{2}+\left(\frac{5}{6}\right)^{4}+\ldots .\right] \\ \end{aligned}

\begin{aligned} &=\frac{5}{36}\left[\frac{1}{1-\frac{25}{36}}\right] \quad\left[1+a+a^{2}+a^{3}+\ldots=\frac{1}{1-a}\right] \\\\ &=\frac{5}{36} \times \frac{36}{11} \\\\ &=\frac{5}{11} \end{aligned}

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