new_contents: 
  # http://code.activestate.com/recipes/511478-finding-the-percentile-of-the-values/
  
  import math
  def percentile(N, percent, key=lambda x:x):
      """
      Find the percentile of a list of values.
  
      @parameter N - is a list of values. Note N MUST BE already sorted.
      @parameter percent - a float value from 0.0 to 1.0.
      @parameter key - optional key function to compute value from each element of N.
  
      @return - the percentile of the values
      """
      if not N:
          return None
      k = (len(N)-1) * percent
      f = math.floor(k)
      c = math.ceil(k)
      if f == c:
          return key(N[int(k)])
      d0 = key(N[int(f)]) * (k-f)
      d1 = key(N[int(c)]) * (c-k)
      return d0+d1
  
  
subject: Update percentile.py