SOLUTION: on professor grindstone final exam the mean score was 78 and the standard deviation 10. he wants to curve the exam so that the middle 50% of students get Cs 1 Find a z score for

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Question 447211: on professor grindstone final exam the mean score was 78 and the standard deviation 10. he wants to curve the exam so that the middle 50% of students get Cs
1 Find a z score for which the area under the standard normal curve from -z to z is 50%
2 find the range of scores which will be assigned a grade of C.
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
on professor grindstone final exam the mean score was 78 and the standard deviation 10. he wants to curve the exam so that the middle 50% of students get Cs
1 Find a z score for which the area under
the standard normal curve from -z to z is 50%
---
Draw the picture.
50% centered at the mean leaves a left tail of 25%
and a right tail of 25%.
Find the z-value that has a 25% left tail:
invNorm(0.25) = -0.6745
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By symmetry the right-tail z-value is +0.6745
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2 find the range of scores which will be assigned a grade of C.
Use x = zs + u to find the scores:
x = -0.6745*10+78 = 71,26
x = +0.6745*10+78 = 84.75
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Cheers,
Stan H.
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