One of the following is missing or broken when we tried to use it: alice, lloyd, tyler, students, get_class_average, get_letter_grade

I expect for the code to work perfectly fine.

```
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]
}
str = "bo"
tyler = {
"name": "Tyler",
"homework": [0.0, 87.0, 75.0, 22.0],
"quizzes": [0.0, 75.0, 78.0],
"tests": [100.0, 100.0]
}
def average(numbers):
total = sum(numbers)/(float)(len(numbers))
return total
def get_average(lloyd):
homework = average(lloyd["homework"])
quizzes = average(lloyd["quizzes"])
tests = average(lloyd["tests"])
return (0.3 * quizzes) + (0.1 * homework) + (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"
print get_letter_grade(get_average(lloyd))
def get_class_average(students):
results = []
results.append(get_average(students))
return results.average()
def get_class_average(students):
results = []
for students in students:
get_average(students)
results.append(get_average(students))
return average(results)
students = [lloyd, alice, tyler]
print get_class_average(students)
print get_letter_grade(get_class_average(students))
```