when to use which formula..?

how do I know when to use


1) z= (x-mu)/standard deviation


or


2) z=(x-mu)/(standard deviation /(n)^(1/2))

Thanks

WlND said:

how do I know when to use


1) z= (x-mu)/standard deviation


or


2) z=(x-mu)/(standard deviation /(n)^(1/2))

Thanks

Click to expand...

When you take a samples of size N from a population distribution, that reduces the uncertainty of the sample mean. The bigger the size of the sample, the better your knowledge of the mean. The standard deviation of sample means is the population standard deviation divided by sqrt(N).