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

```
def average(numbers):
sum(numbers)
total=sum(numbers)
x=float(total)/len(numbers)
return x
def get_average(student):
homework=student["homework"]
quizzes=student["quizzes"]
tests=student["tests"]
x=average(homework)*0.1+average(quizzes)*0.3+average(tests)*0.6
return x
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"
print get_letter_grade(get_average(lloyd))
def get_class_average(class_list):
class_list = [lloyd, alice, tyler]
results = []
for l in class_list:
results.append(get_average(l))
return average(results)
print (get_class_average(class_list))
print (get_letter_grade(average(results)))
```