SOLUTION: on an examination the average grade was 74 and standard deviation was 7 if 10% of the class are given A's and the distribution of grades is to follow a normal distribution then the

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Question 1191900: on an examination the average grade was 74 and standard deviation was 7 if 10% of the class are given A's and the distribution of grades is to follow a normal distribution then the lowest possible A and highest possible B if z10=1.28 is?
Answer by math_tutor2020(3817) About Me  (Show Source):
You can put this solution on YOUR website!

mu = population mean of the class scores = 74
sigma = population standard deviation of the class scores = 7

z10=1.28 indicates the z score for the top 10 percent

This means P(Z > 1.28) = 0.10 approximately

Let's find the raw score x based on this z score
z = (x-mu)/sigma
x-mu = z*sigma
x = mu+z*sigma
x = 74+1.28*7
x = 82.96

The cut off between the highest B and the lowest A is an 82.96
If your teacher is rounding things to the nearest whole number, then it would be an 83.