Z-Scores: Finding the score which separates the top 40% from the bottom 60%?

#1
Hi there I am struggling a little with my z-scores.

This was one of my questions which I do not understand: For a normal distribution with a mean of 100 and an SD of 20, what score separates the top 40% from the bottom 60%?

I have no idea how to work this out and have tried google, looking through the forum so have decided to ask instead.

Any help would be appreciated and how you got to the answer would be even more appreciated!

Many thanks
 

hlsmith

Less is more. Stay pure. Stay poor.
#2
General question, what does plus and minus one standard deviation from the mean represent for area under the normal curve?