A History Teacher Assigns Letter Grades on a Test According $C$

Multiple Choice

A history teacher assigns letter grades on a test according to the following scheme: A: Top 10% B: Scores below the top 10% and above the bottom 60% C: Scores below the top 40% and above the bottom 20% D: Scores below the top 80% and above the bottom 10% F: Bottom 10% Scores on the test are normally distributed with a mean of 69 and a standard deviation of 13.4. Find the numerical limits for each letter grade.

A) A: Above 86
B: Between 72 and 86
$C$ : Between 58 and 71
D: Between 52 and 57
F: Below 52

B) A: Above 81
B: Between 72 and 81
$C$ : Between 58 and 71
D: Between 52 and 57
F: Below 52

C) A: Above 86
B: Between 76 and 86
C: Between 58 and 75
D: Between 52 and 57
F: Below 52

D) A: Above 81
B: Between 72 and 81
C: Between 58 and 71
D: Between 54 and 57
F: Below 54