SOLUTION: (c) It is observed that the average scores on a science test are normally distributed with a mean of 500 and a standard deviation of 80. The scores may have fractional parts. (i)

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Question 829059: (c) It is observed that the average scores on a science test are normally distributed with a mean of 500 and a standard deviation of 80. The scores may have fractional parts.
(i) What proportion of the scores is between 400 and 600? 1 mark
(ii) What value do the upper 10% of the scores exceed?

Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
1.z=%28600-500%29%2F80
z=1.25
P%281.25%29=.8944
You can calculate P%28-1.25%29=0.10565 or use symmetry since P%281.25%29-P%28-1.25%29=2%2A%28P%281.25%29-P%280%29%29
Either way
P%281.25%29-P%28-1.25%29=0.7887
2. Using EXCEL's NORM.INV function for P%28z%29=0.90, then z=602.4