# Suppose a non bias coin was tossed two times?

• Dec 4th 2007, 10:54 PM
jim1174
Suppose a non bias coin was tossed two times?
how would you do a random variable problem like this

suppose a non bias coin was tossed two times
• Dec 4th 2007, 11:06 PM
DivideBy0
Quote:

Originally Posted by jim1174
how would you do a random variable problem like this

suppose a non bias coin was tossed two times

Well... let $x$ be the random variable. You could make it stand for the number of times heads appeared.

$Pr(X=x)$ would then be the probability that x heads appeared.

$Pr(X=0) = 1-\left(\frac{1}{2}\right)^2 = \frac{3}{4}$xxx
$Pr(X=1)=\frac{1}{2}$
$Pr(X=2) = \left(\frac{1}{2}\right)^2 = \frac{1}{4}$

Since the coin is non-biased these same probabilities would appear if you set $x$ as the number of tails that appeared.

Is this what you wanted?
• Dec 5th 2007, 12:06 AM
TwistedOne151
Error
DividyBy0,

Shouldn't it be $Pr(X=0) = \left(1-\frac{1}{2}\right)^2 = \frac{1}{4}$, not $Pr(X=0) = 1-\left(\frac{1}{2}\right)^2 = \frac{3}{4}$ ?

--Kevin C.
• Dec 5th 2007, 12:25 AM
DivideBy0
yeah, you're right