Error: missing parts

```
lloyd = {
"name": "Lloyd",
"homework": [90.0, 97.0, 75.0, 92.0],
"quizzes": [88.0, 40.0, 94.0],
"tests": [75.0, 90.0]
}
alice = {
"name": "Alice",
"homework": [100.0, 92.0, 98.0, 100.0],
"quizzes": [82.0, 83.0, 91.0],
"tests": [89.0, 97.0]
}
tyler = {
"name": "Tyler",
"homework": [0.0, 87.0, 75.0, 22.0],
"quizzes": [0.0, 75.0, 78.0],
"tests": [100.0, 100.0]
}
# Add your function below!
def average(numbers):
total=0
total=total+sum(numbers)
total=float(total)
res=total/len(numbers)
return res
def get_average(student):
homework=average(student["homework"])
quizzes=average(student["quizzes"])
tests=average(student["tests"])
sum=0.10*homework+0.30*quizzes+0.60*tests
return sum
def get_letter_grade(score):
if score>=90:
return "A"
elif score>=80 and score<90:
return "B"
elif score>=70 and score<80:
return "C"
elif score>=60 and score<70:
return "D"
else:
return "F"
get_letter_grade(get_average(lloyd))
def get_class_average(students):
results = []
for student in students:
res=get_average(student)
results.append(res)
return average(results)
students = [lloyd,alice,tyler]
average = get_class_average(students)
print average
print (get_letter_grade(average))
```

Even after this: I am getting the error like: Oops, try again. One of the following is missing or broken when we tried to use it: alice, lloyd, tyler, students, get_class_average, get_letter_grade