Not knowing the actual adjective form means not knowing how to correctly add "ly"

Question

I am a bit frustrated with this lesson.  I guess my question is this: with my limited (A1) knowledge of Spanish, how am I supposed to know "that sometimes the feminine and masculine forms are the same" when repeatedly the test gives adjectives I do not (yet) know in Spanish?  
For example, placid.  I do not KNOW how to say placid in Spanish, thus how can I know if I should use the feminine adjective form or simply add mente?  The assumption of adjective knowledge doesn't work unless, as is sometimes done in the test, you GIVE the adjective form in the test question; example: Los coches son rápidos: van rápidamente.   In this example test question it is easy to understand rápidos (masculine form) will change to the feminine because I can SEE rápidos!  The frustrates me to get wrong when it seems to be testing me more on knowing a large range of adjectives in Spanish more than the specific assignment of adding the "ly" form! I don't see my scores getting better based on the lesson given.

Accepted Answer

Hola Terry
I looked at your recent tests and I can only see one question related to this topic (-mente for regular adverbs. You got this question:

____, te pido que te vayas.
Kindly, I ask you to leave.
(HINT: amable = kind)

There's a hint as you can see, giving you the adjective "amable" so you have the basic form of the adjective. I checked all the questions for this topic and all of them have the hint.
I hope this clarified it for you. 
Saludos y felices fiestas
Inma

Answer

Not the help I was hoping for. I'm really not that interested in my test score as much as I am on how it reflects my understanding of the lesson (I took some guesses on the test and feel I got lucky more than I actually understand, thus my lesson).  Let me try it this way.  When we don't know an adjective AND it doesn't end with an "o" or an "a" (thus hinting at a masculine/feminine descriptive), then we automatically assume the adjective is the type which has feminine and masculine forms the same and thus use "mente"?  If that is the case then I think I get it.  I do appreciate your taking the time to respond and help me get a better understanding on this!