2008-11-25, 06:47 PM
Stereo Wrote:Variance is defined as the average of the squared distance of each term from the mean (for distribution X, and mean mu, sum((x-mu)^2)/size(X) for all x in X)
If you add 2 together, you get that variance(X+Y) = variance(X)+variance(Y)+covariance(X,Y), the standard deviation is the square root of this. Since they're independent (hopefully) you get covariance of zero, meaning the standard deviation over 30 tickets would be sqrt(30*variance(1 ticket)), or sqrt(30)*stdev(1 ticket)
I don't believe that assuming they're equally likely is correct though, it's not true for the easter exp rewards, or the red envelopes at chinese new year.
However if they are, mean is 17084 exp. stdev is 28000 exp. In 30 tickets, that's a mean of 512000 exp, stdev of 153000 exp.
Oh, I get it... kinda.. ish? Haven't started on variance(x+y) and covariance yet, so you lost me there. xD I'll talk about this with mah teacher so I can get a better idea next week. Thanks.
