From wikipedia (http://en.wikipedia.org/wiki/Retroflex_consonant):
"In Swedish and Norwegian, a sequence of r plus a coronal consonant may be replaced by the coronal's retroflex equivalent, e.g. the name Martin is pronounced ['maʈːin] or ['mɑʈːin], and nord ("north") is pronounced [nuːɖ]. This is sometimes done for several consonants in a row after an r — Hornstull is pronounced [huːɳʂ'ʈɵlː])."
Which means that
rn becomes ɳ
rd becomes ɖ
rl becomes ɭ
rs becomes ʂ
Though this differs from different dialects. Here they are is you want to listen to them: http://www.yorku.ca/earmstro/ipa/consonants.html
Both are fine but the standard spelling wordlist SAOL lists it as varsågod and says 'ibland tre ord', which means that they consider both correct but recommend the one word version.
In the course, both are accepted answers but the way the system is built, no spelling variation is accepted in the dictation exercises :(
You might be thinking "ya" means "yes" because of the very Midwestern phrase "ya sure ya betcha." The phrase is pretty much a Scandinavian-American immigrant thing--so the "ya" in this case really is "ja!"
In other words no, "ya" shouldn't work because it's not the English translation of "ja." It's the Swedish equivalent of Spanglish. Swedlish?
Maybe, but English adopts a lot of other slang and vocabulary from other languages. "Ya" is entirely synonymous with "Yes" in the English language, and it wouldn't build any kind of bad habit or misinformation in allowing it as an answer. There is literally no place in any English speaking country(That I'm aware of) that would give a second thought to you responding with "Ya" instead of "Yes". If anything, "Yes" is a little too literal in casual conversation and can sound weird.