Algorithm for selecting N items by price?

Question

PHP

Good day, dear)
Faced the following task:
For example, we have 4 items (it can be as many as you like) and their price
is 1 - 5p
2 - 10p
3 - 5p
4 - 10p
The task is this, select items from here so that they satisfied the condition: the sum of the selected items = 30% (+ -5% (for example) of the total amount of items.
In this case, the following combinations are possible: 1.3 and 2. (The combination with a smaller number of items is in priority)
That is, you need get the combination of items as close as possible to N% of the total amount.Has
anyone come across similar algorithms?
Any examples of solutions/algorithms?
I suppose that first you need to build all combinations without repetitions, and from them already choose the most suitable combination?

Answer 1

The task of laying a knapsack .