This support page describes how to use more than one aggregation type, defining the way the grades are combined, inside the same category.
It is possible that you want the grades from some of your assessed activities to be aggregated together in one way, and the grades from others a different way, but all of them to exist in the same category.
For example, let's say your course has a set of four tests, then one big exam at the end. All of them live in the exam category of Standard Activities. The big exam is 60% of the mark and the remaining 40% comes from the tests, so the weighted mean of grades is fine for the category as a whole. However, you don't want to take a weighted mean of all the tests, you just want to take the highest scoring test and use that one for assessment. So there are two aggregations required, one to drop the lowest scoring tests and take only the highest score forward, and another to take a weighted mean of the score from the tests - which we have decided we want to be the highest scoring test - and the big exam.
The solution is to create another nested category, move the tests into it, and apply a suitable aggregation to that.
Instructions
Step 1 - Create a category for each set of grade items
Step 2 - Set the weighting for each category
This is a powerful tool so if you have any questions - link to moodle docs - link to lt email