input: Write a python function to normalize a list of numbers.
  assert normalize([35, 45, 55, 65, 75]) == [-1.0, -0.5, 0.0, 0.5, 1.0]
  assert normalize([10, 20, 30, 40, 50]) == [-1.2649110640673518, -0.6324555320336759, 0.0, 0.6324555320336759, 1.2649110640673518]
  assert normalize([100, 200, 300, 400, 500]) == [-1.2649110640673518, -0.6324555320336759, 0.0, 0.6324555320336759, 1.2649110640673518]
output: def normalize(lst):
      mean = sum(lst) / len(lst)
      std_dev = (sum((x - mean) ** 2 for x in lst) / len(lst)) ** 0.5
      return [(x - mean) / std_dev for x in lst]