Translation:How do they affect students and teachers?
This is one of the uses of the definite article in Spanish that varies from English. If you are generalizing about the all of something in Spanish you must use the definite article, but in English you never do. The problem is that in all sentences you could theoretically be talking about a specific subset which would require the in English. I think Duo is having a problem coming up with a sentence that is clearly a generalization. The fact that many sentences have multiple possible translations with slightly different meanings is a problem for language instruction. I think I now understand why my earliest French courses in school concentrated on Dialogs, where the context is clear. But the point is that in various situations this sentence may be translated with or without the the, but in any one situation, only one is correct. Duo just wants you to see this as a generalization, although it doesn't really much to hang it on. Report it, but understand the why of the issue.
Spanish has different rules about when the articles are required:
From what I've understood the object pronoun can be omitted under two conditions: 1. The object must come after the verb 2. The object can't be a personal pronoun(yo,ella,ustedes and so on)
pay attention that both conditions are necessary and that even though they can be omitted they are often not.
Yes, because you've used the passive voice with the students and teachers the subject of the sentence; Duolinguo has "they" the subject and the students and teachers the object. Same meaning, but an unnecessary alteration. I'm sure later there will be exercises converting phrases between the active and passive voices... till then, translate what you see.
That is an excellent question and one in which I would love to have a native speaker address. I have tried to find that out on my own, but have only been able to come up with the following link which discusses mixed gender lists with muchos/machas. The responses to the question are not consistent. So I think the answer for a practical matter is, whether there is a rule or not, different people have their own solutions. The question posed however had four items, three of which were feminine. I would assume that would be situation where there might be a different standard usage than this. My sense is that it is not required, but with only two items might well be done. Honestly I have no idea whether the average native speaker could parse a longer list of mixed gendered items into correct groupings while conversing at natural speed. One of the comments talks about the factor that masculine overrides feminine in a mixed group. But as I say, I don't quite see any concensus. But nobody really declared any option as incorrect. But you may be able to get a better picture from this than I.
now matter what i put in, it states that what i have given is the wrong answer. I have tried both ways that the answer could be true, and it states the answer is wrong: I have tried the above translation: How do they affect students and teachers, and it comes back and tells me that it should be how does it affect the students and teachers, when i put that in, it comes back and tells me that the correct answer is: How do they affect students and teachers.
You do seem to have invented the rule of defaulting to ustedes when there is no subject pronoun. At least I have never heard that, nor does it match my experience. There isn't really a default at all. Actually you will probably find subject pronouns on Duo more frequently than in real life because it is the missing context that would have provided the clues needed to determine the intended pronoun. But the closest thing to a default is when there is an abstract genderless it or they. That is what I think what Duo felt that this sentence was demonstrating. If you were discussing various situations and conditions existing in a school and to then ask about their combined effect, I think that is the intended concept here. In that case a subject pronoun would normally not be used. But you are correct. Ustedes should be possible. I often argue against reporting things as errors when they are just Duo trying ineffectually to make a certain point. But here I would definitely say report it. For some reason English speakers tend to have the hardest time recognizing the omitted Ustedes. If someone did teach you that strange rule about ustedes it may simply been a way of tricking you in to remembering to think of ustedes as a translation in the first place.
Would "cómo se afectan a los estudiantes y maestros"
Be "how do students and teachers affect eachother" ?
I know normally when we ask a question with "...a los ___ "... the verb is referring to what goes on with whatever comes after " a los..." so it was a little difficult for me to grasp the translation of this sentence
Your sentence would be Cómo afectan los estudiantes y los profesores el uno al otro or maybe Cómo se afectan los estudiantes y los maestros entre sí. Using the verb reflexively kind of muddied the picture. Strictly speaking this might be considered the personal a. Regardless of the verb, assuming it is transitive, if students and teachers are its direct object, there will be a personal a. But with some verbs like afectar you will see the a used before a direct object that isn't a person or pet more than occasionally. The only input I have gotten about using it with an inanimate object from native speakers is that it sounds funny not to. I think it is a clarity issue. With a verb like afectar which has several meanings but which can take almost anything as a subject or object, I think the a can just add clarity in a language where a subject pronoun can be omitted but a named subject can come before or after the verb. But in a sentence with more context elements, the a would not be used except as a personal a. I may be having a mind block but I can't think of a natural sentence using afectar with an INDIRECT object which are what normally are preceded with a.
It's not clunky, it's just incomplete. But that's true of all the sentences on Duo. I actually assume they probably doesn't represent people at all. It's more likely to be laws, rules, policies or some other circumstances. If this were a new sentence today, I would probably say "they" were all the school closings due to the coronavirus. But it's really irrelevant what they are. Duo does teach greetings and other set expressions, but most sentences are simply examples of random valid sentences demonstrating various aspects of Spanish vocabulary, grammar and syntax. But since Duo won't be able to anticipate all the things that you will need to say or understand in Spanish, all they can do is teach the formulas so to speak.
Your translation is actually the passive voice version of this sentence it would be Cómo son afectados los estudiantes y maestros. If you notice the a in Duo's exercise is a personal a which indicates that they are direct objects, but they were the subjects of yours. As an aside, another way your sentence would be phrase uses the se passive with ver. Cómo se ve afectados... The other note would be that in all these examples including Duo's should actually say los estudiantes y los maestros. Repeating the article is standard in Spanish with or not it changes.