def grades_variance(scores):

average = float(grades_average(scores))

variance = 0

for score in scores:

x = float((average - score) ** 2)

variance += x

result = float(variance) / float(len(scores))

return result

print grades_variance(grades)

def grades_std_deviation(variance):

x = grades_variance(variance)

result = float(x) ** 0.5

return result

print grades_std_deviation(grades)

the error says 'float' object is not iterable

- WHY WON'T THIS WORK?
- WHY DO I HAVE TO x = grades_variance(variance) outside the function?

`Replace this line with your code.`