def weighted_average_for(rank)
      above = data[rank.to_i]
      below = data[rank.to_i - 1]
      fractional = rank - rank.floor
      below + ((above - below) * fractional)
    end
def weighted_average_for(rank)
      above = data[rank.to_i]
      below = data[rank.to_i - 1]
      fractional = rank - rank.floor
      below + ((above - below) * fractional)
    end
when rank lands between values, generated a weighted average
 of adjacent values