An English professor assigns letter grades on a test according to the following scheme. A: Top 5% of scores B: Scores below the top 5% and above the bottom 64% C: Scores below the top 36% and above the bottom 23% D: Scores below the top 77% and above the bottom 9% F: Bottom 9% of scores Scores on the test are normally distributed with a mean of 78.8 and a standard deviation of 7.1. Find the numerical limits for a D grade. Round your answers to the nearest whole number, if necessary.

Grade D score:

Step-by-step explanation:

We are given the following information in the question:

Mean, μ = 78.8

Standard Deviation, σ = 7.1

We are given that the distribution of scores on test is a bell shaped distribution that is a normal distribution.

Formula:

D: Scores below the top 77% and above the bottom 9%

We have to find the value of x such that the probability is 0.77

Calculation the value from standard normal z table, we have,  

We have to find the value of x such that the probability is 0.09

Calculation the value from standard normal z table, we have,  

Thus, the numerical value of score to achieve grade D is

Step-by-step explanation:

A)y=8

B)k=10

5y=72-32

5y=40

y=8

1/2k+24=29

k+48=58

k=58-48

k=10