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Q. 12  Find the probability of throwing at most 2 sixes in 6 throws of a single die.

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Let X represent number of times getting 2 six  in 6 throws of a die.

Probability of getting 6 in single throw of die=P

        P=\frac{1}{6}

        q=1-P=1-\frac{1}{6}=\frac{5}{6}

X has a binomial distribution,n=6

\therefore \, \, \, \, P(X=x)=^nC_x.q^{n-x}.p^x

                P(X=x)=^6C_x.(\frac{5}{6})^{6-x} . (\frac{1}{6})^{x}

                    P(getting\, \, atmost\, \, two\, six)=P(X\leq 2)

                                                                  =P(X=0)+P(X=1)+P(X=2)

                                                                    =^{6}C_0 (\frac{5}{6})^{6}\frac{1}{6}^0+^{6}C_1 (\frac{5}{6})^{5}\frac{1}{6}^1+^{6}C_2 (\frac{5}{6})^{4}\frac{1}{6}^2

                                                                      =1.(\frac{5}{6})^{6}+6. (\frac{5}{6})^{5}\frac{1}{6}+15 (\frac{5}{6})^{4}\frac{1}{36}

                                                                      =(\frac{5}{6})^{6}+ (\frac{5}{6})^{5}+ (\frac{5}{6})^{4}\frac{5}{12}

                                                                  =(\frac{5}{6})^{4}( \frac{5}{6}^{2}+ \frac{5}{6}+\frac{5}{12})

                                                               =(\frac{5}{6})^{4}( \frac{25}{36}+ \frac{5}{6}+\frac{5}{12})

                                                             =(\frac{5}{6})^{4}( \frac{70}{36})

                                                            =(\frac{5}{6})^{4}( \frac{35}{18})

Posted by

seema garhwal

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