SOLUTION: This is a statistics problem, Can someone help? I am so confused. An instructor gives a 100 point exam in which the grades are normally distributed. The mean is 60 and the stan

Question 78380: This is a statistics problem, Can someone help? I am so confused.
An instructor gives a 100 point exam in which the grades are normally distributed. The mean is 60 and the standard deviation is 10. If there are 5% A's and 5% F's, 15% B's and 15% D's and 60% C, find the scores that divide the distribution into those categories
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
An instructor gives a 100 point exam in which the grades are normally distributed. The mean is 60 and the standard deviation is 10. If there are 5% A's and 5% F's, 15% B's and 15% D's and 60% C, find the scores that divide the distribution into those categories.
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The z-score below which 5% of the scores lie is -1.64485
The z-score above which 5% of the scores lie is +1.64485
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Convert these z-scores to raw scores as follows:
x-60=-1.64485*10
x=60-16.4485
x=43.55 (this is the grade score below which 5% of the grades lie)
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x-60=.64485*10
x=60+16.4485
x=76.4485 (this is the grade score above which 5% of the grades lie)
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Follow the same procedure for the other percentages.
Let me know if you have trouble with this.
cheers,
Stan H.

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