Why does mixing up your practice beat drilling one thing at a time?
The practice that feels messier and harder is usually the one that sticks.
Interleaving means shuffling different problem types together instead of doing a long block of one type. Blocked practice feels smoother because you reuse the same method every time, but mixed practice forces you to decide which method each problem needs - and that is exactly what a real test asks. The mixing feels worse yet produces stronger memory and transfer days later.
Doing 10 multiplication then 10 division questions feels easy; jumble them and each one makes you stop and pick the right move - which is how the exam actually comes.
If practice feels too smooth, you are probably blocking; shuffle the types and let it feel harder.
When you study a new skill, rotate question types instead of grinding one - this app interleaves your reviews on purpose.
Mixed feels worse, sticks better.
Learn the idea and practice English at the same time.