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Home  >>  CBSE XII  >>  Math  >>  Probability
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The probability of guessing correctly at least 8 out of 10 answers on a true-false type examination is

$\begin{array}{1 1} (A)\;\large\frac{7}{64}\\(B)\;\large\frac{7}{128}\\(C)\;\large\frac{45}{1024}\\(D)\;\large\frac{7}{41}\end{array} $

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1 Answer

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  • In true or false question
  • p=p(getting correct answer)=\(\frac{1}{2}\)
  • q=1-\(\frac{1}{2}\)=\(\frac{1}{2}\)
  • \(p(x=r)-c^n_r\;p_r\;q_{n-r}\;n=10\)
p(x>8)=p(getting 8 or more question correct)
 \(\Large\frac{1}{28} [45+10+1]=\frac{56}{28} \)
B -option is correct


answered Feb 19, 2013 by poojasapani_1
edited Mar 14, 2013 by poojasapani_1

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