SOLUTION: A teacher informs her history class that a test is very difficult, but the grades would be curved. Scores for the test are normally distributed with a mean of 25 and a standard de

Question 424232: A teacher informs her history class that a test is very difficult, but the grades would be curved. Scores for the test are normally distributed with a mean of 25 and a standard deviation of 5. If the grades are curved according to the following scheme, find the numerical limits for each grade.
A: Top 10%
B: Scores above the bottom 70% and below the top 10%.
C: Scores above the bottom 30% and below the top 30%
D: Scores above the bottom 10% and below the top 70%
F: Bottom 10%

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
A teacher informs her history class that a test is very difficult, but the grades would be curved. Scores for the test are normally distributed with a mean of 25 and a standard deviation of 5. If the grades are curved according to the following scheme, find the numerical limits for each grade.
A: Top 10%
Find z-value with a 10% right tail: 1.2816
Corresponding grade: g = 1.2816*5+25 = 31.41
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B: Scores above the bottom 70% and below the top 10%.
z-value with 30% right tail: 0.5244
Corresponding grade: g = 0.5244*5+25 = 27.62
Ans: grades from 25.62<= g <=31.41
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C: Scores above the bottom 30% and below the top 30%
Can you figure it?
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D: Scores above the bottom 10% and below the top 70%
Can you figure it?
---
F: Bottom 10%
z-value with 10% left tail: -1.2816
Corresponding grade: g = -1.2816*5+25 = 18.59
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Cheers,
Stan H.

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