A teacher informs her organic chemistry class (of 500+ students) that a test was

Question

A teacher informs her organic chemistry class (of 500+ students) that a test was very difficult, but the grades would be curved. Scores on the test were normally distributed with a mean of 28 and a standard deviation of 9.1. The maximum possible score on the test was 100 points. Because of partial credit, scores were recorded with 1 decimal point accuracy. (Thus, a student could earn a 28.1, but not a 27.21.)

The grades are curved according to the following scheme. Find the numerical limits for each letter grade, in interval form:

Explanation / Answer

a)for top 10% ; z score =1.2816

hence corresponding score =mean +z*std deviation=39.7

hence for grade A: score should be greater then 39.7

for 65% ; z score =0.3853

hence corresponding score =mean +z*std deviation=31.5

hence for grade B: score should be between 31.5 and 39.7

for 35% ; z score =-0.3853

hence corresponding score =mean +z*std deviation=24.5

hence for grade C: score should be between 24.5 and 31.5

for 10% ; z score =-1.2816

hence corresponding score =mean +z*std deviation=16.3

hence for grade D: score should be between 16.3 and 24.5

for grade F score should be less then 16.3

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