input: Write a function to normalize a list of numbers.
  assert normalize_list([10, 20, 30, 40, 50]) == [0.0, 0.25, 0.5, 0.75, 1.0]
  assert normalize_list([5, 15, 25, 35, 45]) == [0.0, 0.25, 0.5, 0.75, 1.0]
  assert normalize_list([3, 6, 9, 12, 15]) == [0.0, 0.25, 0.5, 0.75, 1.0]
output: def normalize_list(numbers):
      min_val = min(numbers)
      max_val = max(numbers)
      return [(x - min_val) / (max_val - min_val) for x in numbers]