input: Write a function to calculate the average, maximum, and minimum of a list of integers.
  assert calculate_avg_max_min([1, 7, 4, 6]) == (4.5, 7, 1)
  assert calculate_avg_max_min([10, 20, 30, 40, 50]) == (30.0, 50, 10)
  assert calculate_avg_max_min([5, 3, 9, 1]) == (4.5, 9, 1)
output: def calculate_avg_max_min(lst):
      avg = sum(lst) / len(lst)
      max_val = max(lst)
      min_val = min(lst)
      return (avg, max_val, min_val)