This involved primarily middle-eastern students, from Saudi Arabia, or perhaps elsewhere in that region. They'd apparently get together and each of them work one problem of the homework. Then, when one was wrong, they all had it wrong.

My math instructor pointed out that this was obvious, and what was done to deal with it was that, rather than collecting and grading worked problems, he simply assigned problems on Monday, and gave a quiz on Thursday, which always turned out to be one of the problems, or nearly identical to one. If one had actually worked the assigned problems, it was not problem to handle the quiz. If one hadn't, however, well ...

We didn't have many east Asian students back then. I remember one Pakistani student, who came to me and asked for help with a research paper. What he wanted, though, was to have me proofread and mark up his paper, not to do his work for him. He offered to compensate me for this, but, I declined, as I'd been a foreigner once, myself, and understood the difficulties of learning to write in a new language. I was 4-5 years younger than the typical student at my level, so I was flattered, somewhat to be asked for any sort of help.

RE