DD is in year 7 and trying some of the past junior challenges paper. She is able to attempt, mostly successfully, about first half to two thirds of the questions. And then getting stuck in the later questions, unable to progress without some clues from us.
They are really nice and interesting problems, but typically not the types covered in classroom lessons.
So the question is, how did your DC build skills in solving such questions? Are there books specifically for such papers? Where can we get more similar quality questions?