Translation:Five hundred yuan
Renminbi is the name of the currency and means 'money of the people'. Yuan is the basic unit of the currency, the coin (or banknote).
It's like in the UK the official name of the currency is 'pound sterling' and the coin is called 'pound'. You would never say 'I have 5 pounds sterling' (renminbi), instead you say 'I have 5 pounds' (yuan). So you don't use Renminbi to indicate an amount of money. However, the other way around 'yuan' is used to refer to the currency as a whole, just as pounds is used to refer to the UK's currency (omitting the 'sterling'). Source: wiki.
For DL: forget renminbi and just use yuan.
Please see my post about "yuan" and 元: https://forum.duolingo.com/comment/25665794?comment_id=38975999