1. ## finding the standard deviation of a radom variable??

can anybody solve this.

2. 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

3. 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

4. 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.