My solution.

mantpaa.MathGame/MathGame.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

mantpaa.MathGame/MathGame.sln

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+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.5.2.0
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "MathGame", "MathGame.csproj", "{8E44D313-4A8D-F5FA-1FB5-C00DA569A7BD}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{8E44D313-4A8D-F5FA-1FB5-C00DA569A7BD}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{8E44D313-4A8D-F5FA-1FB5-C00DA569A7BD}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{8E44D313-4A8D-F5FA-1FB5-C00DA569A7BD}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{8E44D313-4A8D-F5FA-1FB5-C00DA569A7BD}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {BA2070F0-AF12-4B1E-BF4A-511581206CBF}
+	EndGlobalSection
+EndGlobal

mantpaa.MathGame/Models/GameData.cs

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+namespace MathGame.Models;
+
+internal class GameData
+{
+    private int score;
+    private double avgTimePerQuestion;
+    private int difficultyLevel;
+    private Question[] questions;
+
+    public GameData(int score, int difficultyLevel, Question[] questions)
+    {
+        this.score = score;
+
+        this.difficultyLevel = difficultyLevel;
+        this.questions = questions;
+        this.avgTimePerQuestion = CalculateAvgTimePerQuestion();
+    }
+
+    public override string ToString()
+    {
+        string returnString = "";
+        foreach (var question in questions)
+        {
+            returnString += $"Equation: {question.Equation} = ?, Answer: {question.Answer}, Expected answer: {question.ExpectedAnswer}, Time spent: {((question.TimeSpentSeconds) >= 0 ? (question.TimeSpentSeconds) : "N/A")} seconds.\n";
+        }
+        returnString += "".PadLeft(Console.BufferWidth, '-') + "\n";
+        returnString += $"Score: {score}, Difficulty level: {difficultyLevel}, Average time per question: {avgTimePerQuestion} seconds.";
+        return returnString;
+    }
+
+    private double CalculateAvgTimePerQuestion()
+    {
+        int totalTime = 0;
+        int questionsAnswered = 0;
+        foreach (var question in questions)
+        {
+            if (question.TimeSpentSeconds >= 0)
+            {
+                totalTime += question.TimeSpentSeconds;
+                questionsAnswered++;
+            }
+        }
+
+        return questionsAnswered > 0 ? (double)totalTime / questionsAnswered : 0;
+    }
+}

mantpaa.MathGame/Models/GameEngine.cs

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+using System.Diagnostics;
+
+namespace MathGame.Models;
+
+internal class GameEngine
+{
+    string[] operators = new string[] { "+", "-", "*", "/" };
+    List<GameData> gameHistory = new List<GameData>();
+    int difficulty = 1;
+    GameType gameType = GameType.Addition;
+
+    public void PlayGame()
+    {
+        GameData gameData;
+
+        int score = 0;
+
+
+        Console.WriteLine("Starting the game! Answer the following questions:");
+        Console.WriteLine("To give up, type 'exit'.");
+
+        Question[] questions = InitializeGame(difficulty);
+        for (int i = 0; i < questions.Length; i++)
+        {
+            Stopwatch stopwatch = new Stopwatch();
+            stopwatch.Start();
+
+            Console.WriteLine($"Question {i + 1}: {questions[i].Equation}");
+            string? userAnswer = Console.ReadLine();
+            stopwatch.Stop();
+
+            if (userAnswer != null && userAnswer.ToLower() == "exit")
+            {
+                Console.WriteLine("Exiting the game. Goodbye!");
+                break;
+            }
+
+            if (userAnswer != null)
+            {
+                questions[i].Answer = userAnswer;
+                questions[i].TimeSpentSeconds = stopwatch.Elapsed.Seconds;
+                if (userAnswer == questions[i].ExpectedAnswer)
+                {
+                    Console.WriteLine("Correct!");
+                    score++;
+                }
+                else
+                {
+                    Console.WriteLine($"Wrong! The correct answer is {questions[i].ExpectedAnswer}");
+                }
+            }
+        }
+        gameData = new GameData(score, difficulty, questions);
+
+        gameHistory.Add(gameData);
+    }
+
+    public void ViewGameHistory()
+    {
+        Console.WriteLine("Score history:");
+        for (int i = 0; i < gameHistory.Count; i++)
+        {
+            Console.WriteLine($"Game {i + 1}:\n{gameHistory[i].ToString()}\n");
+        }
+        Console.WriteLine("Press any key to continue...");
+        Console.ReadKey();
+        Console.Clear();
+    }
+
+    public void ChangeDifficulty()
+    {
+        string? input;
+        Console.WriteLine("Current difficulty level: " + difficulty);
+        Console.WriteLine("Enter new difficulty level (1-3):");
+        input = Console.ReadLine();
+
+        while (input == null || !new string[] { "1", "2", "3" }.Contains(input))
+        {
+
+            Console.WriteLine("Invalid input, try again.");
+            input = Console.ReadLine();
+        }
+
+        difficulty = int.Parse(input);
+    }
+    public void ChangeQuestionType()
+    {
+        string? input;
+        Console.WriteLine("Enter question type:\na - addition\ns - subtraction\nm - multiplication\nd - division\nr - random!");
+        input = Console.ReadLine();
+
+        while (input == null || !new string[] { "a", "s", "m", "d", "r" }.Contains(input.ToLower()))
+        {
+            Console.WriteLine("Invalid input, try again.");
+            input = Console.ReadLine();
+        }
+
+        switch (input.ToLower()) 
+        {
+            case "a":
+                gameType = GameType.Addition;
+                break;
+            case "s":
+                gameType = GameType.Subtraction;
+                break;
+            case "m":
+                gameType = GameType.Multiplication;
+                break;
+            case "d":
+                gameType = GameType.Division;
+                break;
+            case "r":
+                gameType = GameType.Random;
+                break;
+        }
+    }
+    private Question[] InitializeGame(int difficultyLevel)
+    {
+        Random random = new Random();
+        string[] operatorValue = new string[] { "+", "-", "*", "/" }; // 0:+, 1: -, 2: *, 3: / : GameType enum values correspond to these indices.
+        int questionsToAsk = 5;
+        Question[] questions = new Question[questionsToAsk];
+        for (int i = 0; i < questionsToAsk; i++)
+        {
+            string op = "+";
+
+            if (gameType == GameType.Random)
+            {
+                op = GetOperator(random);
+            }
+            else
+            {
+                op = operatorValue[(int) gameType];
+            }
+
+            questions[i] = CreateQuestion(op, difficultyLevel, random);
+        }
+
+        return questions;
+    }
+
+    private Question CreateQuestion(string op, int difficultyLevel, Random random)
+    {
+        if (op == "/")
+        {
+            int dividend = 1;
+            int divisor = 1;
+            bool valid = false;
+            while (valid == false)
+            {
+                dividend = random.Next(0, 101);
+                int minValue = (difficultyLevel > 1) ? 2 : 1; // disallow division by 1 for higher difficulties.
+                divisor =  random.Next(minValue, (dividend > minValue) ? dividend : minValue +1); // Ensure maxval is larger than minval
+                if (dividend % divisor == 0)
+                {
+                    valid = true;
+                }
+            }
+
+            string equation = $"{dividend} / {divisor}";
+            string expectedAnswer = (dividend / divisor).ToString();
+            return new Question(equation, "", expectedAnswer);
+        }
+
+        else if (new string[] {"+", "*", "-" }.Contains(op))
+        {
+            int num1 = random.Next(1, 10 * difficultyLevel);
+            int num2 = random.Next(1, 10 * difficultyLevel);
+            string equation = $"{num1} {op} {num2}";
+            string expectedAnswer = "";
+            if (op == "+")
+                expectedAnswer = (num1 + num2).ToString();
+            else if (op == "-")
+                expectedAnswer = (num1 - num2).ToString();
+            else if (op == "*")
+                expectedAnswer = (num1 * num2).ToString();
+            else
+                expectedAnswer = "issue occured";
+
+            return new Question(equation, "", expectedAnswer);
+        }
+
+        else
+        {
+            throw new InvalidDataException("Invalid operator: " + op);
+        }
+    }
+
+    // Pick a random operator for the question, to help randomize the questions a bit more.
+    private string GetOperator(Random random)
+    {
+        int val = random.Next(0, operators.Length);
+        return operators[val];
+    }
+
+    enum GameType
+    {
+        Addition,
+        Subtraction,
+        Multiplication,
+        Division,
+        Random
+    }
+}

mantpaa.MathGame/Models/Question.cs

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+namespace MathGame.Models;
+
+internal class Question
+{
+    public string Equation { get; set; }
+    public string Answer { get; set; }
+
+    public string ExpectedAnswer { get; set; }
+
+    public int TimeSpentSeconds { get; set; } = -1; // Todo: better value?
+    public Question(string equation, string answer, string expectedAnswer)
+    {
+        Equation = equation;
+        Answer = answer;
+        ExpectedAnswer = expectedAnswer;
+    }
+
+}

mantpaa.MathGame/Program.cs

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+using MathGame.Models;
+
+namespace MathGame;
+
+public static class MathGame
+{
+    public static void Main()
+    {
+        GameEngine gameEngine = new GameEngine();
+
+        string input = "";
+        do
+        {
+            Console.WriteLine("Math game!\n" +
+                "Press the number to choose a menu option.\n"+
+                "1. Play game\n"+
+                "2. See history.\n"+
+                "3. Change difficulty(1-3).\n"+
+                "4. Change question type\n"
+                +"Exit to exit.");
+            string? userInput = Console.ReadLine();
+
+            if (userInput != null)
+            {
+                input = userInput.ToLower();
+                switch (input)
+                {
+                    case "1":
+                         gameEngine.PlayGame();
+                        break;
+                    case "2":
+                        gameEngine.ViewGameHistory();
+                        break;
+                    case "3":
+                        gameEngine.ChangeDifficulty();
+                        break;
+                    case "4":
+                        gameEngine.ChangeQuestionType();
+                        break;
+                    case "exit":
+                        Console.WriteLine("Exiting the game. Goodbye!");
+                        break;
+                    default:
+                        Console.WriteLine("Invalid input, try again.");
+                        Console.WriteLine("Press any key to continue...");
+                        Console.ReadKey();
+                        Console.Clear();
+                        break;
+                }
+            }
+        } while (input != "exit");
+    }
+}