"Je suis rapide."
Translation:I am fast.
I am surprised, I can't figure out any situation where "rapide" could mean strong or steep... except if you are talking about statistics, where a "strong/steep increase" would be (mis)interpreted by "rapide", but frankly, "une augmentation forte / soutenue" would be much better.
Rapide is the common form for masculine and feminine singular.
For your info, a few adjectives that already have an ending -e in masculine: vide, fade, dupe, rare, âcre, apre, pire, sage, sage, fixe, pauvre, large, calme, arabe, tiède, raide, acide, aride, avide, beige, belge, rouge, riche, moche, sale, ovale, noble, frêle, drôle, ample, digne, terne, jaune, avare, sobre, obèse, dense, lisse, leste, juste, vague, brave...
I had no idea of the point you made here. I am very new to Duolingo and am astounded by its scope and potential. I love the stories and look forward to seeing how DL develops and matures. I have a U3A class of fifteen septuagenarians who keep me on my toes. You will probably "meet" them soon when they start to take part in these discussions. How about some items with some context...short paragraphs? Thank YOU for your tact and erudition.
The architecture of the course does not allow for paragraphs, not even long sentences.
You and your students will have to get used to translating the French sentences in the most direct way, even if more idiomatic translations would feel more natural to you, English speakers.
Some sentences in English can look a bit awkward but be aware that they are already translations from French and their structure should give you hints on how to back-translate these to proper French (ideally the original sentence).
The forums are available for users to ask questions to other users (including Moderators). Before asking a question, you will first read the whole thread to see whether an answer is already available or not.
If you do not understand why your translation was rejected (by the computer which compares your translation with those we have listed in the database), you will write it down entirely (because nobody can see what is happening during your working session) so that we can see what was wrong (sometimes the system focuses on one error and there is another one).
Happy learning to you and your students!