input: Write a function to find the maximum and minimum numbers in a list.
  assert get_max_min([-5, 7, 2, 11, -9]) == (11, -9)
  assert get_max_min([1, 2, 3, 4, 5]) == (5, 1)
  assert get_max_min([10, 10, 10]) == (10, 10)
output: def get_max_min(lst):
      return (max(lst), min(lst))