**Answer:**

import statistics as st **# importing statistics package to calculate mean as st.**

grades = {"John": [87,90,86.8], "Mary": [78, 81.5, 88.6],"Susan":[45,67,76]}

for key,value in grades.items():**#iterating over the dictionary**

average_score=st.mean(value)**#calculating the mean of every student**

gr="" ** empty string to store the grades**

if average_score>=90: **# nested if else if and statements for the grades in gr**

gr="A"

elif average_score>=80.0 and average_score<90.0:

gr="B"

elif average_score>=70.0 and average_score<80.0:

gr="C"

elif average_score>=60.0 and average_score<70.0:

gr="D"

else :

gr="F"

print(str(key)+" "+str(average_score)+" "+str(gr)) **#printing grades of every student.**

**Output:-Mary 82.7 B
**

**John 87.93333333333334 B
**

**Susan 62.666666666666664 D**

**Explanation:**

1.In this program we are iterating over the **dictionary grades.**

2.Storing and calculating the **mean** of the scores of every student us **statistics package**.

3.Storing the grade in **string gr **and updating the **gr **according to the mean score

4.After that printing the grade of the student with their name and mean score.