input: Write a function to calculate the sum, mean, and median of a given list.
  assert calculate_statistics([1, 2, 3, 4, 5]) == (15, 3.0, 3)
  assert calculate_statistics([1, 2, 3, 4, 5, 6]) == (21, 3.5, 3.5)
  assert calculate_statistics([7, 8, 9, 10, 11]) == (45, 9.0, 9)
output: def calculate_statistics(lst):
      n = len(lst)
      sum_lst = sum(lst)
      mean_lst = sum_lst / n
      sorted_lst = sorted(lst)
      
      if n % 2 == 0:
          median_lst = (sorted_lst[n//2 - 1] + sorted_lst[n//2]) / 2
      else:
          median_lst = sorted_lst[n//2]
          
      return sum_lst, mean_lst, median_lst