There is plenty of research* showing that interleaving maths practise helps students learn. This means that a mixed set of questions on different topics is more effective than a big block of questions which require the same technique over and over again.
It’s one thing to know that this is what the research says and another thing to put this into practise in the classroom. Textbooks are still written with sets of near identical exercises and it’s much easier for a busy teacher to point students at a page in a text book than to prepare a set of mixed questions of the right difficulty.
Where can busy teachers find sets of well written questions requiring a mix of techniques? Exam papers! As well as the exam boards many schools have end of year tests and publish past papers on their websites. So go forth, shamelessly borrow, and let your students reap the rewards of interleaved practise.