## random var. X is -1, 0, 1 w/ equal probability (check ans)

Standard deviation, mean, variance, z-scores, t-tests, etc.
zorro
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Joined: Sat Jun 12, 2010 9:26 am
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### random var. X is -1, 0, 1 w/ equal probability (check ans)

Question :
X is a random variable which takes 3 values -1,0,1 with equal probability i.e. P(x=-1) = P(X=0) = P(X=1) = 1\3
Find E(X) and Var(X)
Solution :
E(X) = 0 (is this correct?)

var(X) = 0 (is this correct?)

Martingale
Posts: 350
Joined: Mon Mar 30, 2009 1:30 pm
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### Re: random var. X is -1, 0, 1 w/ equal probability (check an

zorro wrote:Question :
X is a random variable which takes 3 values -1,0,1 with equal probability i.e. P(x=-1) = P(X=0) = P(X=1) = 1\3
Find E(X) and Var(X)
Solution :

ok...

zorro wrote:E(X) = 0 (is this correct?)

Yes

zorro wrote:var(X) = 0 (is this correct?)

No

zorro
Posts: 28
Joined: Sat Jun 12, 2010 9:26 am
Contact:

### Re: random var. X is -1, 0, 1 w/ equal probability (check an

Please can u tell what is wrong

My work ........
E(X) = 0

$\mu'$ 1 = 0

$\mu'$ 2= 2/3

$\mu$2 = 2/3

var(X) = $\mu'$2 - $\mu$2 = 2/3 - 2/3 = 0

Martingale
Posts: 350
Joined: Mon Mar 30, 2009 1:30 pm
Location: USA
Contact:

### Re: random var. X is -1, 0, 1 w/ equal probability (check an

zorro wrote:Please can u tell what is wrong

My work ........
E(X) = 0

$\mu'$ 1 = 0

$\mu'$ 2= 2/3

$\mu$2 = 2/3

var(X) = $\mu'$2 - $\mu$2 = 2/3 - 2/3 = 0

$Var(X)=E(X^2)-[E(X)]^2=E(X^2)-0^2=E(X^2)=2/3$

zorro
Posts: 28
Joined: Sat Jun 12, 2010 9:26 am
Contact:

### Re: random var. X is -1, 0, 1 w/ equal probability (check an

Martingale wrote:
zorro wrote:Please can u tell what is wrong

My work ........
E(X) = 0

$\mu'$ 1 = 0

$\mu'$ 2= 2/3

$\mu$2 = 2/3

var(X) = $\mu'$2 - $\mu$2 = 2/3 - 2/3 = 0

$Var(X)=E(X^2)-[E(X)]^2=E(X^2)-0^2=E(X^2)=2/3$

Thanks !!!