The following table shows the probability of rolling the numbers 1 through 7 on a fair seven-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?"

Question

The following table shows the probability of rolling the numbers 1 through 7 on a fair seven-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?"

anonymous · Answer

1/7 ?
im not sure about deviation

anonymous · Answer

lol me neither...but i know its a decimal i forgot how to do the work for this...

anonymous · Answer

nvmmmm its 2.0 !
gah..

shadowfiend · Answer

It's kind of a pain, but to find the standard deviation you have to square the difference of each point to the mean, then find the mean of those numbers, and finally take the square root.

I think in this case we would see a mean of 4 ((1+2+3+4+5+6+7)/7). So you'd square 1-4, 2-4, 3-4, 4-4, etc, then add those up and divide by 7 to find their mean, then take the square root of that (which will indeed get you 2).

anonymous · Answer

I remember now! Thanks