〔２０分〕請問有無人可以示範一次點樣計variance同covariance?

concept: is correct!!
variance 可以用黎計一堆數o既分散程度
variance越大即d數分得越散
but: doesnt seem correct!
covariance係計兩堆數之間o既分散程度

my idea:
we use covariance between two randow variances and which indicates how variables vary to each other. in other words, if the convariance is postive, as one variable increased the other tends to increase. otherwise, as one variance increase the other tends to decrease. however, if the covariance is zero, the value of one variable is unaffected by the other ( it means they are independent)

hope it helps!

2007-11-07 00:49:54 補充：
is'' random'' not randow

甲班={30,80,50,65,10}
mean=(30+80+50+65+10)/5=47

variance:
=(30^2+80^2+50^2+65^2+10^2)/5 - 47^2
=(900+6400+2500+4225+100)/5 - 2209
=2825 - 2209
=616

乙班={95,85,10,40,45}
mean=(95+85+10+40+45)/5=55

variance:
=(95^2+85^2+10^2+40^2+45^2)/5 - 55^2
=(9025+7225+100+1600+2025)/5 - 3025
=3995 - 3025
=970