For a long time, in the north, a hundred was a hundred and twenty. Old Norse hundrað counted twelve tens, so “two hundred” meant two hundred and forty, and anyone who needed the plain hundred we use now had to say which hundred they meant. The second half of the word, the -rað, meant reckoning, so the number carried its own instructions for counting folded up inside it. English kept the word and quietly let the extra twenty go. Nobody remembers agreeing to that, which is how most bargains with a word get made.