```
Replace this line with your code.
def grades_std_deviation(variance):
variance = variance **0.5
variance = grades_variance(grades)
print grades_std_deviation(variance)
Oops, try again. grades_std_deviation(6.25) returned None instead of the expected: 2.5
```

# Standard deviation

**navikrish**#1

Please read the instructions CAREFULLY.

They say:

1.Define a function grades_std_deviation(variance).

You did that.

2.return the result of variance ** 0.5

You did not return variance = variance ** 0.5

3.After the function, create a new variable called variance and store the result of calling grades_variance(grades).

It says AFTER the function, which means, NOT nested under it. So, "variance = grades_variance(grades)" must be outside the function "grades_std_deviation(variance)"

4.Finally print the result of calling grades_std_deviation(variance).

You did that.

Final code should look like that:

```
def grades_std_deviation(variance):
return variance ** 0.5 #return, not just type "variance ** 0.5"
variance = grades_variance(grades) #under the function, not nested
print grades_std_deviation(variance)
```

**fiske_d**#4

"Who needs to pay for grade calculation software when you can write your own? :)"

Does anyone actually do this?? What is the American obsession with grades and grade averages? Bizzare...