<PRE><B>Question 1151477</B>
z-score formula is defined as
:
z-score = (X - mean)/standard deviation
:
standard deviation = square root of variance, for this problem
:
standard deviation = square root(25) = 5
:
z-score = (80 - 90)/5 = -2
:
Note to find the probability associated with this z-score, you lookup the z-score in the table of z-scores
:
If your table of z-scores is only for positive values, then lookup the probability associated with, in this case, 2.  Then subtract that value from 1 to get the probability associated with -2
:
Why do you think this works?
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