In task is wrong formula.

**04** for each score in scores: Compute its squared difference: (**average - score**) ** 2 and add that to variance.

Correct formula should be:

(**score - average**) ** 2

Mathematical formula:

(1/Number of occurrences) * Summation (sigma symbol) i = 1 to Number of occurrences (xi - average) **2

link:https://en.wikipedia.org/wiki/Variance

Code:

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