Hi!

I am learning Python and I am in Exam Statistic lesson, Standard Deviation

the link to the exercise - https://www.codecademy.com/courses/learn-python/lessons/exam-statistics/exercises/standard-deviation?action=resume_content_item

it is pretty straight forward exerecise, so I wrote down the following code and in the monitor a message says error:

Traceback (most recent call last): File “python”, line 30, in <module> File “python”, line 27, in grades_std_deviation TypeError: unsupported operand type(s) for ** or pow(): ‘list’ and ‘float’

my code:

```
grades = [100, 100, 90, 40, 80, 100, 85, 70, 90, 65, 90, 85, 50.5]
def print_grades(grades_input):
for grade in grades_input:
print grade
def grades_sum(scores):
total = 0
for score in scores:
total += score
return total
def grades_average(grades_input):
sum_of_grades = grades_sum(grades_input)
average = sum_of_grades / float(len(grades_input))
return average
def grades_variance(scores):
average = grades_average(scores)
variance = 0
for score in scores:
variance += (average - score)**2
variance = variance / float(len(scores))
return variance
def grades_std_deviation(variance):
return variance ** 0.5 #line 27
variance = grades_variance(grades)
print grades_std_deviation(grades)# line 30
```

when I checked the solution to this exercise, they did the same thing in def grades_std_deviation.

can you help me understand what I did wrong?

Thank you!