Help with a second year stats question? Best answer will be awarded.

GRE scores are normally distributed with a mean μ = 500 and a standard deviation of σ = 100. A sample of size n = 25 is drawn from this distribution.

What is the first quartile of the sampling distribution of the mean?

Okay so I know the first quartile is the first 25%, and I know I need to use z scores and such.

I set up my equation liiiike 0.25 = (y-500) / 20. The 20 comes from the standard deviation (100) divided by the square root of n (25). So if I solve algebraically I get 505. Is this right? Do I need the actual z score for the first quartile?

Standard deviation of sampling distribution = σ/√n = 100/√25 = 100/5 = 20
That's ok

Now we use z-score table to find z-score such that P(z http://www.regentsprep.org/Regents/math/…
P(z < -0.675) = 0.25

So now we c