I wrote the code according to what the instructions said to do, but it keeps giving me the error

Oops, try again.

`grades_variance([4, 4, 3, 5, 6, 7, 1, 7])`

returned 0.048828125 instead of the expected: 3.734375

Please tell me whats wrong with my code.

```
grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]
def print_grades(grades):
for grade in grades:
print grade
def grades_sum(grades):
total = 0
for grade in grades:
total += grade
return total
def grades_average(grades):
sum_of_grades = grades_sum(grades)
average = sum_of_grades / float(len(grades))
return average
def grades_variance(scores):
average = grades_average(scores)
variance = 0
for score in scores:
variance += ((average - score) ** 2)
variance /= float(len(scores))
return variance
print(grades_variance(grades))
```