Question

A philosophy professor assigns letter grades on a test according to the following scheme. A: Top 12% of scores B: Scores below the top 12% and above the bottom 57% C: Scores below the top 43% and above the bottom 19% D: Scores below the top 81% and above the bottom 5% F: Bottom 5% of scores Scores on the test are normally distributed with a mean of 66.5 and a standard deviation of 9.9. Find the minimum score required for an A grade. Round your answer to the nearest whole number, if necessary.

Answer 1

The minimum score required for an A grade is 80.

Explanation:

According to the Question,

• Given That, A philosophy professor assigns letter grades on a test according to the following scheme.

A: Top 12% of scores

B: Scores below the top 12% and above the bottom 57%

C: Scores below the top 43% and above the bottom 19%

D: Scores below the top 81% and above the bottom 5%

F: Bottom 5% of scores Scores on the test

And The normally distributed with a mean of 66.5 and a standard deviation of 9.9.

Now,

• In a set with mean and standard deviation, the Z score of a measure X is given by Z = (X-μ)/σ

we have μ=66.5 , σ=9.9

• Find the minimum score required for an A grade.

Top 12%, so at least the 100-12 = 88th percentile, which is the value of X when Z has a p-value of 0.88. So it is X when Z = 1.175.

⇒ Z = (X-μ)/σ

⇒ 1.175×9.9 = X-66.5

⇒ X=78.132

Rounding to the nearest whole number, the answer is 80.

The minimum score required for an A grade is 80.