SOLUTION: 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%

Question 1053959: 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.
Mainly, I don't understand how to do this:
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.
How do you find the 1.64485? Step by step processes will be helpful for everything!
Thank you!
Answer by ewatrrr(24785) (Show Source): You can put this solution on YOUR website!
Need to Know:
z = invNorm(Percentage). Percentage listed as a decimal for arithmetic purposes.
That Percentage being to the Area under the standard Normal Curve to the left of that z - value
Ex: Just a Visual of areas left of the Green Lines for various z-values

mean is 60 and the standard deviation is 10
top score: invNorm(.05) = -1.64485 Use Calculator
0r
Top F score
least score: invNorm(.95) = 1.64485 Calculator

|
least score: one more than Top F score
top score: invNorm(.20)= z

|
least score: one more than top D .
top score:invNorm(.80) =z

|
least score: one more than top C .
top score: One less than bottom A score

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