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 29 and a standard deviation of 8.7. 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 29.7, but not a 28.18.)

The grades are curved according to the following scheme. Find the numerical limits for each letter grade.

Letter Scheme Interval A Top 6% B Scores above the bottom 66%
and below the top 6% C Scores above the bottom 34%
and below the top 34% D Scores above the bottom 6%
and below the top 66% F Bottom 6%

Explanation / Answer

a) Top 6% = NORMSINV(0.94)*8.7+29 = 42.5

(42.5, 100)

B) Scores above the bottom 66% = NORMSINV(0.66)*8.7+29=32.6

(32.6, 42.5)

C) Scores above the bottom 34% = NORMSINV(0.34)*8.7+29=.25.4

(25.4, 32.6)

D) Scores above the bottom 6% = NORMSINV(0.06)*8.7+29 = 15.5

(15.5, 25.4)

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