Browse Questions

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

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

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

edited Jun 4, 2013