Question 469024

Z = (x-u)/s, where u=mean, s=std deviation
The probabilities given always are for less than or equal to that number.
**********************************
8. you used 1 instead of -1:
Always subtract the mean, if its smaller you should get a negative Z
For Z = -1, P = .1587
*********************************
9. Look at question, they want scores greater than 590.
For Z= 1.5, P = .9332
So 93% are less, the compliment is 1-P
1-P = .0668
**********************************
10. Don't subtract Z values, only P values
Take P from 590 and subtract P from 440
.9332 - .1587 = .7745
********************************
11. Top 20% also means that at that score 80% will be less than that score.
Find Z such that P=0.8
Corresponding Z is .8416
Find x using this value.
(x-500)/60 = .8416
x-500 = 50
x = 550