80 percent percent = 0.008. The two tailed z-score for 0.008 is 2.652
z = 0.8416
Let your raw score be x and M the mean and S the standard deviation. The Z score for your specific x is Z=(x-M)/S So say your score is 80 (out of 100) and the mean is 70 and the standard deviation is 10. Then the z score for your 80 is: (80-70)/10=1 If on the other hand you got a 60, then the z score would be -1.
The Z-value for a one-sided 91% confidence interval is 1.34
The answer depends on whether the confidence interval is one sided or two sided.
Pr{z<=1.0805}~=0.86
-0.38532
It is -0.51
z = 1.28, approx.
1.96
1.15
ss
norminv([(1-0.86)/2 1 - (1-0.86)/2], 0, 1) which results in a z-score range of -1.4758 to 1.4758