The hints are wrong for 적이. (2017-09-18)
Also, 온 here does not mean whole. It is actually 오다+ㄴ.
It literally means [I do] not have the experience of coming here.
They're throwing a lot of grammar in this one. So many grammar points. If anyone is using only Duolingo and is new to Korean, this is probably a nightmare.
I agree, THIS ONE lesson is a nightmare, and it's strength drops more fastly than any others... So it sucks
Yeah its obvious theyve got some kinks to work out. Im glad this isnt my sole way to study (dont think that would be possible actually)