Exercise: Student becomes teacher

Error: 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

Help! Code runs but throws the above Code Academy error. I have gone through the posts where users have encountered similar error and checked for the possible solutions. What am i overlooking in the below code?

```
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]
}
students = [lloyd, alice, tyler]
def average(numbers):
total=sum(numbers)
total = float(total)
total = total / len(numbers)
return total
def get_average(student):
homework = average(student["homework"])
quizzes = average(student["quizzes"])
tests = average(student["tests"])
return 0.1*homework + 0.3*quizzes + 0.6*tests
def get_letter_grade(score):
if score >=90:
return "A"
elif score >=80:
return "B"
elif score >=70:
return "C"
elif score>=60:
return "D"
else:
return "F"
def get_class_average(students):
results =[]
for student in students:
results.append(get_average(student))
return average(results)
average=get_class_average(students)
print average
print get_letter_grade(average)
```