"جورْج أُسْتاذ أَمْريكِيّ مُمْتاز."

Translation: George is an amazing American professor.

[joelp]

I couldn't find information about the -un ending in the tips. Why does the noun and first adjective have it but the second adjective NOT have it?

[Christoph55835]

There are some rules about when and when not to pronounce case endings. In spoken Arabic, people don't use them in most cases anyway. In Modern Standard Arabic (MSA) it's OK to omit the case ending at the end of a sentence (that's the case here) or in pausa.

[joelp]

Thanks for that. arabic.desert-sky.net has pretty good article on case endings but I'm sure there is plenty of useful information about this subject out there.

[benton.1]

Also, case endings are not used after names that are not Arabic.

[MOHAMMADIB640942]

My answer was correct

[MagyRosman]

So why i got an error if i used teacher instead of professor?

[benton.1]

Because "teacher" and "professor" are two different words both in English and Arabic.