An unbiased coin is tossed n times and X is the number of heads obtained. Write down an expression for the probability that X=r.(adsbygoogle = window.adsbygoogle || []).push({});

It looks so simple yet I cant figure it out.

Does it follow a binomial distribution ?

Then if

[tex]

X[/tex]~[tex]N (n,p)[/tex]

It follows

[tex]

P(X=r) = \left(

\begin{array}{cc}

n\\

r

\end{array}

\right)

\cdot p^r \cdot q^{n-1} [/tex]

where [tex]q=1-p[/tex]

But [tex] p=q=1/2

[/tex]

So the answer is

[tex]

P(X=r) = \left(

\begin{array}{cc}

n\\

r

\end{array}

\right)

\frac{1}{2}^{r+n-1}[/tex]

Am I right ?

P.S. First time using latex. It sure took long. :tongue2:

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# Homework Help: Simple Probability Question

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