input: Write a function to calculate the average of five numbers entered by a user.
  assert calculate_average([10, 20, 30, 40, 50])==30.0
  assert calculate_average([5, 15, 25, 35, 45])==25.0
  assert calculate_average([2, 4, 6, 8, 10])==6.0
  assert calculate_average([1, 3, 5, 7, 9])==5.0
  assert calculate_average([0, 0, 0, 0, 0])==0.0
output: def calculate_average(numbers):
      return sum(numbers) / len(numbers)