finding the standard deviation of a radom variable??

**arslan** · April 29th 2009, 10:50 AM

can anybody solve this.

**Moo** · April 29th 2009, 10:55 AM

Originally Posted by arslan

can anybody solve this.

Compute $\mathbb{E}(X)=\sum_{i=1}^3 x_i \mathbb{P}(X=x_i)=0.2 \times 10+0.3\times 20+0.5\times 30$

Complete the table with the values of x^2
Then compute $\mathbb{E}(X^2)=\sum_{i=1}^3 x_i^2 \mathbb{P}(X=x_i)$

The variance is $\mathbb{E}(X^2)-[\mathbb{E}(X)]^2$

That's all folks

**arslan** · April 29th 2009, 11:08 AM

Originally Posted by Moo

Compute $\mathbb{E}(X)=\sum_{i=1}^3 x_i \mathbb{P}(X=x_i)=0.2 \times 10+0.3\times 20+0.5\times 30$

Complete the table with the values of x^2
Then compute $\mathbb{E}(X^2)=\sum_{i=1}^3 x_i^2 \mathbb{P}(X=x_i)$

The variance is $\mathbb{E}(X^2)-[\mathbb{E}(X)]^2$

That's all folks

i dont quite get where do i go once i do 10x0.2+20x0.3+30x0.5 = 23

**mr fantastic** · April 29th 2009, 04:40 PM

Originally Posted by arslan

i dont quite get where do i go once i do 10x0.2+20x0.3+30x0.5 = 23

You go and do the second and third things that you were told in post #2.

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