using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    private static int[] categoryIds = new int[] {1, 2, 3, 4, 5};

    private static int[] questionsPerCategory = {3, 1, 6, 11, 7};

    //Part of demo

    private static IEnumerable<QuestionVM> Questions = Enumerable.Range(0, 100).Select(x=> new QuestionVM { Question = $"Question - {x}", CategoryId = (x % 5) + 1});

    public static void Main()

    {

        var questions = Questions.Where(x=> x.InTest).GroupBy(x=> x.CategoryId).SelectMany(x=> x.OrderBy(y=> Guid.NewGuid()).Take(GetQuestionTake(x.Key)));

        foreach(var question in questions)

            Console.WriteLine($"{question.Question} - CategoryId: {question.CategoryId}");  

    }

    ///Finds out how many questions it should take by doing a search and then picking the element in the same position

    private static int GetQuestionTake(int categoryId)

    {

        int element =  categoryIds.Select((x, i) => new { i, x }).FirstOrDefault(x => x.x == categoryId).i;

        return questionsPerCategory.ElementAtOrDefault(element);

    }

}

​

​

//Part of demo

public class QuestionVM

{

    public string Question {get;set;}

    public int CategoryId {get;set;}    

    public bool InTest {get;set;} = true;

}