The mean of a normal probability distribution is 380; the standard deviation is 10.
a. About 68% of the observations lie between what two values?
About 95% of the observations lie between what two values?
Practically all of the observations lie between what two values?
a. 68% of the observations lie between the z scores of -1 to +1
Now, z= X - mean/s.d
So, here X= +-1*S.D + mean
So X = 370, 390
Hence 68% of the values lie between 370 to 390
b. 95% of the values lie between z-score of +-1.96
So, here X= +-1.96*10 + 380
So X= 360.4, 399.6
So 95% of the values lie between 360.4 to 399.6
c. About 100% of the values should lie between the z score of +-3
So, X= 350, 410
So practically all the values should lie between 350 to 410
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