I'll send this to SraJMcGin, aka Mme.
First of all, I would need to see the directions to know what you were supposed to do. What I see is l'imparfait but I don't know if that is what you were to do.
1. I would not like the word "un job" because in what sense? There is more than one word for "job" but it depends upon the context.
un travail - a piece of work
une besogne/une tâche - a chore
un emploi - employment
un travail à forfait - work done under contract
2. same word
With l'imparfait you have said "had" & "were working/used to work"
Sra (aka Mme)
These are the instructions:
Quand ils étaient à l’université, certains étudiants avaient un job et travaillaient. D’autres ne travaillaient pas. Expliquez cela.
And Here are the examples:
Il n’avait pas de job. Il ne travaillait pas.
Elle avait un job. Elle travaillait dans une boutique.
When I see "Expliquez cela" I would expect that you have to explain WHY some have jobs and some do not. Give a reason , in each case.
Sra (aka Mme)
The terrible thing about textbooks is that it's not enough to be able to read and understand the text. You ALSO have to be able to read and understand the question about the text. If you cannot understand the question that is asked, it doesn't matter that you DO understand the text that you read.
One issue that arises here, as you mentioned, is pluralization. "Some had a job. Some didn't." In fact, some had jobs; some didn't. It wasn't that several people had the same job. And yet, although there is not number agreement, the sentence is still grammatically acceptable. Compare in English, "You both have a job." with "You both have jobs." Neither is wrong although one uses the plural and one uses the singular, both to express the same thing.
The simple solution is to say, "We both are employed." That removes the confusion and resolves the question of agreement in number. The verb "are" has to agree with the pronoun "we" and not with "jobs" or "employment."
"We have a job" is colloquial, informal speech that means, "We both have jobs." It certainly doesn't mean, "We both share one job."