I'm working on Lesson 7: Variance: https://www.codecademy.com/courses/python-intermediate-en-7mgOa/2/1?curriculum_id=4f89dab3d788890003000096

The error message I'm getting is this:

Oops, try again.

grades_variance([0, 8, 0]) returned 14 instead of the expected: 14.2222222222

I've run it several times, and the list in the error message will have more or less items, such as

```
Oops, try again.
grades_variance([6, 5, 7, 5, 6, 3, 5, 3]) returned 1 instead of the expected: 1.75
```

or

Oops, try again.

grades_variance([5, 4]) returned 0 instead of the expected: 0.25

Here's my code, which I've literally copied from another thread to be sure it's correct:

```
[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 / len(grades)
return average
def grades_variance(scores):
average = grades_average(scores)
variance = 0
for score in scores:
variance += (average - score) ** 2
result = variance/len(scores)
return result
print grades_variance(grades)
```

Am I doing something wrong, or is this some kind of glitch? I have no idea how to identify a pattern in those error messages.