input: Write a python function to compute the average value in an array.
  assert computeAverage([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]) == 5.5
  assert computeAverage([10, 20, 30, 40, 50]) == 30.0
  assert computeAverage([5, 15, 25, 35, 45]) == 25.0
output: def computeAverage(arr):
      return sum(arr) / len(arr)