SOLUTION: For a normal distribution with mean of 100 and standard deviation of 20, find the following: a) The score that separates the lower 20% of the cases from the upper 80%

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Question 509791: For a normal distribution with mean of 100 and standard deviation of 20, find the following:
a) The score that separates the lower 20% of the cases from the upper 80%
b) The number of cases that fall between the values of 110 and 120.
c) The number of cases that fall between 90 and 120.
d) The number of cases that fall above a score of 80.
Answer by stanbon(75887) (Show Source):
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For a normal distribution with mean of 100 and standard deviation of 20, find the following:
a) The score that separates the lower 20% of the cases from the upper 80%
Find the z-score with a left tail of 0.20
invNorm(0.2) = -0.8416
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Find the corresponding raw score value:
x = z*s+u
x = -0.8416*20+100 = 83.17
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b) The percent of cases that fall between the values of 110 and 120.
Find the corresponding z-values.
Then find the percentage between those z-values.
Ans: 0.1499
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c) The percent of cases that fall between 90 and 120.
Ans: 0.5328
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d) The percent of cases that fall above a score of 80.
Ans: 0.8413
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Cheers,
Stan H.