"""Solution 18.3.2 — Average of three grades

Chapter 18: Bugs — Everyday Programming

Bug type: Logical

Operator precedence divides only c by 3 before adding, so the result is
wrong. Parenthesizing the sum before dividing computes the true average.

Exercise: ex_18_3_2.py
"""

def average(a, b, c):
    return (a + b + c) / 3

print(average(80, 90, 100))   # 90.0