Statistics Question

[Skanky Burns]

How do I find out the probability of a random sample of n=15 having a mean of +1 standard deviation of the population mean?

I've been trying all day to work this one out, but it has continued to give me problems.

[KrazyHorse]

The standard deviation of the mean of a random sample of a population with normal distribution drops as the square root of the size of the sample.

In other words, a sampling of 15 people at random from the population will give a mean which is normally distributed about the population mean with standard deviation 1/sqrt(15) times the population standard deviation.

So the probability of your fifteen people having mean equal to or greater than 1 sigma is the same as the probability of taking an individual and having him be equal to or greater than sqrt(15) sigma = 3.87 sigma or so (0.01% or so IIRC)

[KrazyHorse]

This is a standard random walk problem...

[Skanky Burns]

Its what I get for not studying this though.
Cheers.