I've heard some mathematics teachers don't think it is in the syllabus.Is derangements even in the syllabus???
Pretty sure it's not seeing as they had to give us the definition.
It's really stupid to put that in the exam because the only ones able to answer it are those that luckily studied it. Unless someone's a genius and understood everything he needed to do from a 1 line definition and answered everything with the amount of time we were given.
It's in cambridge 3u, one of the challenge exercises in perms/combs.I can say that I've never done any derangement question before that paper (unless there was a BoS trial one that I forgot about). It gave you all necessary definitions and the concept wasn't very difficult. I actually felt like the last question was way too easy, it spoon fed every step - "show ..." then like 1 step "show ..." over and over.