No, but the 'y' sound in Mandarin is difficult because it is not the full and drawn out 'y' of the American English word of 'yes,' but is closer to the 'i' in machine, but with glide that makes it sound y-ish. My guess is that you hear a 'g' because the sound is strange for a 'y,' or the Duolingo staff fixed it before I got here.
That's right! That reminds me, 美金 (mei2 jin1) is also used to refer to the currency, but there isn't really ”日金“，or ”英金“，for example.
More 'trivia': you can (colloquially) refer to 50 cents as 五角钱 (wu2 jiao3 qian2) or 五毛钱 (wu3 mao2 qian2).
Good to know:
Note that the pronunciation of the first 五 is not the original 第三声 (di3 san1 sheng1, ie the third tone), but 第二声 (er4, the second tone), since the character that follows is also 第三声. This is a rule for pronunciation.
Yuan is 'units' of currency. So it could be used for other currencies ...I was told. However, if another currency is actually specified then I'd suggest that should be used intranslation. In normal language 'kwai' is used. BUt the correct name for the currency is renminbi (peoples' money). Yeah, I know, internationally, the word yuan is normally used. See also: https://ask-a-chinese-guy.blogspot.com/2010/12/rmb-yuan-and-kwai.html
It's not simple, but you can be sure it's a unit for currency. Please see my post for more details: https://forum.duolingo.com/comment/25665794?comment_id=38975999
It can be ten Euro-dollars, too. Please see my post about the 元 character: https://forum.duolingo.com/comment/25665794?comment_id=38975999