I want somebody to tell me, do my workings follow the correct method? I'm fairly certain they do but I want another opinion. Thanks.
Assume the scores on an aptitude are normally distributed with mean=500 and standard deviation=100
What is the middle 40%?
from statistical tables
=> z2= -0.525 z1= 0.525
z1=(x-500)/100=0.525 => x=500+52.5=552.5
z2=(x-500)/100=-0.525 => x=500-52.5=447.5
therefore the middle 40% is between 447.5 and 552.5.
Now my question. Is that the correct method and approach, it is a bonus if I got it right. I only want to check the method really. Thanks.