Check a string to see if it is a valid Australian Business Number

ABNCheck.rb

# Algorithm taken from ATO website.
def valid_abn?(abn)
  WEIGHTS = [10,1,3,5,7,9,11,13,15,17,19]
  tmpabn = abn.split("").map{|c| c.to_i}
  tmpabn[0] = tmpabn[0] - 1
  checksum = (0..10).inject(0) do |sum, i|
    sum + (tmpabn[i].to_i * WEIGHTS[i])
  end
  return (checksum % 89) == 0
end