Question

what z score value separates teh highest 20% of the scores from the rest of the distribution

Answer 1

Essentially, this means that the very rightmost part of the normal distribution will hold 20% of the distribution, or the leftmost part will contain 80%. That is you are finding \(P(Z\ge z)=0.2\), or equivalently, \(P(Z\le z)=0.8\). You need the normal distribution cdf table to do so.

Answer 2

The value of z should be about 0.845