It's automatically accepted by Duolingo, through a flawed list of "synonyms".
We've already complained about it to the powers that be, but we cannot change it ourselves.
I'm not sure where you're seeing the word "storey." It's not an accepted answer.
Here is a link to the screenshot , if that is ok to post here. https://www.dropbox.com/s/eufaq26ew5n407y/Screenshot_2015-12-13-19-26-16.png?dl=0 link should now work, dropbox in doesn't require special permissions like google disk to view pictures
That looks really strange.
(Your mistake was using the plural form, stories, however.)
yes I know, most of the time I am writing really fast plus those letters on touch-screen keyboard are really small. I was instantly confused when I saw "storey"
Nei...... storey ˈstɔːri/Submit noun a part of a building comprising all the rooms that are on the same level. "a three-storey building" synonyms: floor, level, tier; More