diff --git a/Recursion/Recursion.csproj b/Chapter4_QuickSort/Chapter4_QuickSort.csproj
similarity index 100%
rename from Recursion/Recursion.csproj
rename to Chapter4_QuickSort/Chapter4_QuickSort.csproj
diff --git a/Chapter4_QuickSort/Program.cs b/Chapter4_QuickSort/Program.cs
new file mode 100644
index 0000000..65b9f80
--- /dev/null
+++ b/Chapter4_QuickSort/Program.cs
@@ -0,0 +1,19 @@
+// Задача 4.1 - сумма массива в виде рекурсивной функции
+int[] arr = [1, 2, 3];
+Console.WriteLine($"4.1. Сумма: [{string.Join(", ", arr)}] равна {Task4_1.Calculate(arr)}");
+
+// Задача 4.2 - количество элементов в списке в виде рекурсивной функции
+LinkedList<int> list = new LinkedList<int>([10, 20, 30, 40, 50]);
+Console.WriteLine($"4.2. Количество элементов в списке: {Task4_2.Count(list.First!)}");
+
+// Задача 4.3 - поиск максимального элемента в LinkedList с помощью рекурсии
+// Пример: находим максимум в списке [7, 2, 9, 4, 5]
+LinkedList<int> list2 = new LinkedList<int>([7, 2, 9, 4, 5]);
+Console.WriteLine($"4.3. Максимум в списке: {Task4_3.Max(list2.First!)}");
+
+// Задача 4.4 - бинарный поиск в отсортированной коллекции с помощью рекурсии
+int[] sortedArr = [10, 20, 30, 40, 50, 60];
+int target = 42;
+int index = Task4_4.BinSearch(sortedArr, target, 0, sortedArr.Length - 1);
+Console.WriteLine($"4.4. Индекс числа {target} в массиве: {index}");
+
diff --git a/Chapter4_QuickSort/Task4_1_Sum.cs b/Chapter4_QuickSort/Task4_1_Sum.cs
new file mode 100644
index 0000000..4a1ca63
--- /dev/null
+++ b/Chapter4_QuickSort/Task4_1_Sum.cs
@@ -0,0 +1,9 @@
+static class Task4_1
+{
+    public static int Calculate(int[] arr, int index = 0)
+    {
+        if (index == arr.Length - 1)
+            return arr[index];
+        return arr[index] + Calculate(arr, index+1);
+    }
+}
\ No newline at end of file
diff --git a/Chapter4_QuickSort/Task4_2_Count.cs b/Chapter4_QuickSort/Task4_2_Count.cs
new file mode 100644
index 0000000..0ebb6f0
--- /dev/null
+++ b/Chapter4_QuickSort/Task4_2_Count.cs
@@ -0,0 +1,9 @@
+static class Task4_2
+{
+    public static int Count<T>(LinkedListNode<T> listNode, int currentLen = 0)
+    {
+        if (listNode.Next != null)
+            return Count(listNode.Next, currentLen + 1);
+        return currentLen + 1;
+    }
+}
\ No newline at end of file
diff --git a/Chapter4_QuickSort/Task4_3_Max.cs b/Chapter4_QuickSort/Task4_3_Max.cs
new file mode 100644
index 0000000..a417df4
--- /dev/null
+++ b/Chapter4_QuickSort/Task4_3_Max.cs
@@ -0,0 +1,10 @@
+static class Task4_3
+{
+    public static int Max(LinkedListNode<int> listNode, int currMax = int.MinValue)
+    {
+        currMax = Math.Max(currMax, listNode.Value);
+        if (listNode.Next != null)
+            return Max(listNode.Next, currMax);
+        return currMax;
+    }
+}
\ No newline at end of file
diff --git a/Chapter4_QuickSort/Task4_4_BinSearch.cs b/Chapter4_QuickSort/Task4_4_BinSearch.cs
new file mode 100644
index 0000000..b337f70
--- /dev/null
+++ b/Chapter4_QuickSort/Task4_4_BinSearch.cs
@@ -0,0 +1,16 @@
+static class Task4_4
+{
+    public static int BinSearch(IEnumerable<int> collection, int target, int left, int right)
+    {
+        if (left > right)
+            return left; // позиция для вставки
+
+        var mid = (left + right) / 2;
+        var value = collection.ElementAt(mid);
+        if (value == target)
+            return mid;
+        if (value < target)
+            return BinSearch(collection, target, mid + 1, right);
+        return BinSearch(collection, target, left, mid - 1);
+    }
+}
\ No newline at end of file
diff --git a/GrokAlgorithms.sln b/GrokAlgorithms.sln
index b59c8ce..7b69c3f 100644
--- a/GrokAlgorithms.sln
+++ b/GrokAlgorithms.sln
@@ -3,7 +3,7 @@ Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio Version 17
 VisualStudioVersion = 17.0.31903.59
 MinimumVisualStudioVersion = 10.0.40219.1
-Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Recursion", "Recursion\Recursion.csproj", "{7F895D96-6E79-40BC-A778-89E76BC981F6}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Chapter4_QuickSort", "Chapter4_QuickSort\Chapter4_QuickSort.csproj", "{4088F633-80E4-44DF-9DE4-996A4B3E3088}"
 EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
@@ -18,5 +18,13 @@ Global
 		{7F895D96-6E79-40BC-A778-89E76BC981F6}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{7F895D96-6E79-40BC-A778-89E76BC981F6}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{7F895D96-6E79-40BC-A778-89E76BC981F6}.Release|Any CPU.Build.0 = Release|Any CPU
+		{C4C54C0A-59E1-4C40-B2C2-D8C800603AF6}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{C4C54C0A-59E1-4C40-B2C2-D8C800603AF6}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{C4C54C0A-59E1-4C40-B2C2-D8C800603AF6}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{C4C54C0A-59E1-4C40-B2C2-D8C800603AF6}.Release|Any CPU.Build.0 = Release|Any CPU
+		{4088F633-80E4-44DF-9DE4-996A4B3E3088}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{4088F633-80E4-44DF-9DE4-996A4B3E3088}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{4088F633-80E4-44DF-9DE4-996A4B3E3088}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{4088F633-80E4-44DF-9DE4-996A4B3E3088}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 EndGlobal
diff --git a/Recursion/Program.cs b/Recursion/Program.cs
deleted file mode 100644
index d0bc281..0000000
--- a/Recursion/Program.cs
+++ /dev/null
@@ -1,2 +0,0 @@
-Console.WriteLine("Hello, World!");
-