## Grade book
Complete the function so that it finds the mean of the three scores passed to it and returns the letter value associated with that grade.
Numerical Score    | Letter Grade
---                | ---
90 <= score <= 100 | 'A'
80 <= score < 90   | 'B'
70 <= score < 80   | 'C'
60 <= score < 70   | 'D'
 0 <= score < 60   | 'F'
Tested values are all between 0 and 100. Theres is no need to check for negative values or values greater than 100.
def get_grade(s1, s2, s3):
    mean = sum([s1,s2,s3])/3
    if mean>=90: return 'A'
    if mean>=80: return 'B'
    if mean>=70: return 'C'
    if mean>=60: return 'D'
    return 'F'

def get_grade(s1, s2, s3):
    mean = sum([s1,s2,s3])/3
    if mean>=90: return 'A'
    if mean>=80: return 'B'
    if mean>=70: return 'C'
    if mean>=60: return 'D'
    return 'F'
