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Probability

Question
CBSEENMA12033843

Find the probability of getting 5 exactly twice in 7 throws of a die.

Solution

Here,   n = 7
          p =  P(5) = 1 over 6 comma   straight q space equals space 1 minus 1 over 6 space equals 5 over 6
P(exactly twice) = straight P left parenthesis 2 right parenthesis space equals space straight C presuperscript 7 subscript 2 space space open parentheses 5 over 6 close parentheses to the power of 5 space open parentheses 1 over 6 close parentheses squared space equals space fraction numerator 7 cross times 6 over denominator 1 cross times 2 end fraction cross times 5 to the power of 5 over 6 to the power of 5 cross times 1 over 6 squared space equals space 21 space open parentheses 5 to the power of 5 over 6 to the power of 7 close parentheses.

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