Question

The following table shows the probability of rolling the numbers 1 through 7 on a fair 7-sided die.

X 1 2 3 4 5 6 7
P(X) 1/7 1/7 1/7 1/7 1/7 1/7 1/7
What is the standard deviation of the random variable X, "the number that comes up on the die"?
A. 3.745
B. 1.708
C. 2.0
D. 3.5
E. 2.917

Answer 1

For a discrete variable:
\(\huge \sigma_x ^2=\Sigma~(x_i\mu_x)^2P(x_i)\)
I suppose you already know how to find \(\mu_x\)

Answer 2

nope

Answer 3

Typo:
\(\huge \sigma_x ^2=\Sigma~(x_i-\mu_x)^2P(x_i)\)

Answer 4

Well, the mean is:
\(\huge \mu_x=\Sigma x_iP(x_i)\)

Answer 5

oh okay