Calculating Mean and Standard Deviation for a Biased Die Rolled 2000 Times

[matadorqk]

Homework Statement

A die is biased such that the probability of getting a six is 1/4. The die is rolled 2000 times. Let X be the number of sixes obtained. Find,

a) the mean of X
b) the standard deviation of X, leaving your answer as a surd.

Homework Equations

The Attempt at a Solution

a) The mean of X is simple, given P(6)=1/4, and the dice is rolled 2000 times, the mean of X is 2000(1/4)=500

b) This is where I don't know what to do. Any guidance?

 

[CompuChip]

It's simply a binomial distribution.