def mean(numbers_ary)
      numbers_ary.inject(0) { |sum, i| sum + i }.to_f / numbers_ary.size
    end
def mean(numbers_ary)
      numbers_ary.inject(0) { |sum, i| sum + i }.to_f / numbers_ary.size
    end
Simple mean formula: sum elements and / by length

 @param numbers_ary [array] an array of numbers to calculate the mean

 @return [float]

 @example
   Exonio.mean([1,2,3,4,5]) # => 3.0