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Home  >>  CBSE XII  >>  Math  >>  Probability

Eight coins are tossed together.The probability of getting exactly 3 heads is

$\begin{array}{1 1}(A)\;\frac{1}{256}\quad(B)\;\frac{7}{32}\quad(C)\;\frac{5}{32}\quad(D)\;\frac{3}{32}\end{array} $

1 Answer

Toolbox:
  • probability of getting head in a toss p=\(\Large\frac{1}{2}\)
  • q=1-\(\Large\frac{1}{2}\)=\(\Large\frac{1}{2}\)
  • 8 coins are tossed n=8
  • \(p(X=r)=c^n_r\;p^r\;q^{n-r}\)
\(\Large\;n=8\; r=3\)
\(\Large\frac{8\times7\times6}{1\times2\times3}\)\(\times\)\(\Large\frac{1}{28}\)
\(\Large56\times\frac{1}{28}\)
\(\Large\frac{7}{32}\)
'b'option is correct

 

answered Feb 19, 2013 by poojasapani_1
edited Jun 4, 2013 by poojasapani_1
 

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