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Home  >>  CBSE XII  >>  Math  >>  Probability
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A die is thrown three times.Let X be 'the number of twos seen'.Find the expectation of X.

$\begin{array}{1 1}(A)\;\large\frac{1}{2}\\(B)\;\large\frac{1}{4}\\(C)\;\large\frac{1}{8}\\(D)\;\large\frac{1}{3}\end{array} $

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  • Die is thrown 3 times
  • Probability of getting '2'=\(\frac{1}{6}\)in a single through of die
  • P=\(\frac{1}{6}\)q=1-\(\frac{1}{6}\)=\(\frac{5}{6}\)
  • X=defined as number '2'2seen
  • X=(\(0\;1\;2\;3\))
  • E(X)=\(\sum\)P\(_i\)X\(_i\)
  • \(P(x-r\))=\(^n\)C\(_r\) P\(^r\) q\(^{n-r}\)
answered Feb 27, 2013 by poojasapani_1

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