input: Write a python function to get the average of a list of numbers.
  assert get_average([2, 4, 6, 8]) == 5.0
  assert get_average([1, 3, 5, 7, 9]) == 5.0
  assert get_average([10, 20, 30, 40, 50]) == 30.0
output: def get_average(numbers):
      return sum(numbers) / len(numbers)