# Standard deviation of a random variable

• August 8th 2007, 12:44 PM
earachefl
Standard deviation of a random variable
I believe the answer given is wrong for the following question:

Quote:

Determine the mean and standard deviation of the random variable whose probability distribution is
x = 2, P(x) = .1
x = 4, P(x) = .2
x = 6, P(x) = .4
x = 8, P(x) = .2
x = 10, P(x) = .1
My answer is $\mu = 6, \sigma \approx 2.28$. The book says that $\sigma = 2.19$. Who's right?
• August 8th 2007, 12:51 PM
CaptainBlack
Quote:

Originally Posted by earachefl
I believe the answer given is wrong for the following question:

My answer is $\mu = 6, \sigma \approx 2.28$. The book says that $\sigma = 2.19$. Who's right?

The book (assuming you have $\mu$ right).

RonL
• August 8th 2007, 01:10 PM
earachefl
argghhh.... stupid math error....