Challenge questions from FPM quizzes: GCD1

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Perhaps it would be interesting to post some of my so-called "challenge" questions from my FPM quizzes. I won't post them all at once. Here, as a png image, is the very first "challenge" question I set them, on GCDs (Greatest Common Divisors, also known as Highest Common Factors). It is just a screenshot, so the buttons don't do anything. Enjoy!
Quiz question
Screenshot of "challenge" question from FPM First Quiz on GCDs

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