input: Write a python function to calculate the average of a list of numbers.
  assert calculate_avg([1, 2, 3, 4, 5]) == 3
  assert calculate_avg([10, 20, 30, 40, 50]) == 30
  assert calculate_avg([5, 15, 25, 35, 45]) == 25
output: def calculate_avg(numbers):
      return sum(numbers) / len(numbers)