How to find out all numbers from all variations with the minimum number of operations?

Question

Algorithms

We have 100 known numbers (12 56 84 15, etc.) and there is a single number, for example 40. We need to find all variations of 10 known numbers whose average will be less than a single number 40

Answer 1

First you need to weed out all variants of the means ( heuristics ).
To do this, you need to know:
1. Can numbers be repeated
2. What does it mean (a system of inequalities): the average for N numbers in relation (greater/less) to the given one.

Answer 2

Backpack packing problem.
The average less than 40 is the same as the sum less than 400.
Well, then there is nothing much better than enumeration.