Random Variables Question Help Please!!!!!?

Please help me with this question...I've tried all kinds of ways of solving this but none of the numbers add up. Please let me know how you did it. Thank You!!!





The following table shows the probability of rolling the numbers 1 through 6 on a fair die.





X 1 2 3 4 5 6


P(X) 1/6 1/6 1/6 1/6 1/6 1/6





What is the standard deviation of the random variable X, "the number that comes up on the die?"





A. 1.708


B. 2.917


C. 14.028


D. 3.745


E. 3.5

Random Variables Question Help Please!!!!!?
The expected value i.e. mean is 3.5 so you will have to sum the squares 2.5^2 1.5^2 .5^2 (twice) divide by 6 and take the sqaure root. Ithink it comes out at A)
Reply:Okay you need to calculate standard deviation =sqrt(%26lt;x^2%26gt;-%26lt;x%26gt;^2). You know the average value of x, %26lt;x%26gt;=3.5. Now you just have to calculate the average squared value which is just %26lt;x^2%26gt;=(1+4+9+16+25+36)/6. Plug that in and you're done.