diff --git a/lab6/Makefile b/lab6/Makefile
index 93456b0..a90496f 100644
--- a/lab6/Makefile
+++ b/lab6/Makefile
@@ -1,4 +1,4 @@
-.PHONY: run build clean task1 build-task1 clean-task1 task2 build-task2 clean-task2 task3 build-task3 clean-task3 task4 build-task4 clean-task4 task5 build-task5 clean-task5 task6 build-task6 clean-task6 task7 build-task7 clean-task7 task8 build-task8 clean-task8 task9 build-task9 clean-task9 task10 build-task10 clean-task10 task16 build-task16 clean-task16 task17 build-task17 clean-task17 task18 build-task18 clean-task18 task19 build-task19 clean-task19
+.PHONY: run build clean task1 build-task1 clean-task1 task2 build-task2 clean-task2 task3 build-task3 clean-task3 task4 build-task4 clean-task4 task5 build-task5 clean-task5 task6 build-task6 clean-task6 task7 build-task7 clean-task7 task8 build-task8 clean-task8 task9 build-task9 clean-task9 task10 build-task10 clean-task10 task16 build-task16 clean-task16 task17 build-task17 clean-task17 task18 build-task18 clean-task18 task19 build-task19 clean-task19 task20 build-task20 clean-task20
 
 # task1
 run:
@@ -151,3 +151,13 @@ build-task19:
 
 clean-task19:
 	cd task19 && dotnet clean
+
+# task20
+task20:
+	cd task20 && dotnet run --project task20.fsproj
+
+build-task20:
+	cd task20 && dotnet build
+
+clean-task20:
+	cd task20 && dotnet clean
diff --git a/lab6/task20/Program.fs b/lab6/task20/Program.fs
new file mode 100644
index 0000000..06f7e9f
--- /dev/null
+++ b/lab6/task20/Program.fs
@@ -0,0 +1,219 @@
+open System
+
+let vowels = set ['a'; 'e'; 'i'; 'o'; 'u'; 'A'; 'E'; 'I'; 'O'; 'U'; 
+                  'а'; 'е'; 'и'; 'о'; 'у'; 'ы'; 'э'; 'ю'; 'я'; 
+                  'А'; 'Е'; 'И'; 'О'; 'У'; 'Ы'; 'Э'; 'Ю'; 'Я']
+
+let isVowel c = vowels.Contains(c)
+let isConsonant c = Char.IsLetter(c) && not (isVowel c)
+
+let englishFrequency = Map.ofList [
+    ('a', 8.12); ('b', 1.49); ('c', 2.78); ('d', 4.25); ('e', 12.02);
+    ('f', 2.23); ('g', 2.02); ('h', 6.09); ('i', 6.97); ('j', 0.15);
+    ('k', 0.77); ('l', 4.03); ('m', 2.41); ('n', 6.75); ('o', 7.51);
+    ('p', 1.93); ('q', 0.10); ('r', 5.99); ('s', 6.33); ('t', 9.06);
+    ('u', 2.76); ('v', 0.98); ('w', 2.36); ('x', 0.15); ('y', 1.97); ('z', 0.07)
+]
+
+let sortByCriteria1 (strings: string[]) =
+    strings
+    |> Array.sortBy (fun str ->
+        let chars = str.ToCharArray()
+        let vowelCount = chars |> Array.filter isVowel |> Array.length
+        let consonantCount = chars |> Array.filter isConsonant |> Array.length
+        let vowelAvg = if vowelCount > 0 then float vowelCount / float str.Length else 0.0
+        let consonantAvg = if consonantCount > 0 then float consonantCount / float str.Length else 0.0
+        abs (consonantAvg - vowelAvg))
+
+let sortByCriteria2 (strings: string[]) =
+    strings
+    |> Array.sortBy (fun str ->
+        let chars = str.ToCharArray()
+        let avgAscii = chars |> Array.map (fun c -> float (int c)) |> Array.average
+        avgAscii)
+
+let sortByCriteria3 (strings: string[]) =
+    strings
+    |> Array.sortBy (fun str ->
+        let chars = str.ToCharArray()
+        let charCounts = chars |> Array.countBy id |> Map.ofArray
+        let mostFrequentChar, maxCount = charCounts |> Map.toArray |> Array.maxBy snd
+        let stringFreq = float maxCount / float str.Length
+        let alphabetFreq = 
+            match englishFrequency.TryFind (Char.ToLower mostFrequentChar) with
+            | Some freq -> freq / 100.0
+            | None -> 0.01
+        abs (stringFreq - alphabetFreq))
+
+let sortByCriteria4 (strings: string[]) =
+    if strings.Length = 0 then strings
+    else
+        let firstStringAvgAscii = 
+            strings.[0].ToCharArray() 
+            |> Array.map (fun c -> float (int c)) 
+            |> Array.average
+        
+        strings
+        |> Array.sortBy (fun str ->
+            let avgAscii = str.ToCharArray() |> Array.map (fun c -> float (int c)) |> Array.average
+            (avgAscii - firstStringAvgAscii) ** 2.0)
+
+let sortByCriteria5 (strings: string[]) =
+    strings
+    |> Array.sortBy (fun str ->
+        let chars = str.ToCharArray()
+        let charCounts = chars |> Array.countBy id |> Map.ofArray
+        let mostFrequentChar, maxCount = charCounts |> Map.toArray |> Array.maxBy snd
+        let stringFreq = float maxCount / float str.Length
+        let expectedFreq = 
+            match englishFrequency.TryFind (Char.ToLower mostFrequentChar) with
+            | Some freq -> freq / 100.0
+            | None -> 0.01
+        (stringFreq - expectedFreq) ** 2.0)
+
+let sortByCriteria6 (strings: string[]) =
+    let mutable sortedStrings = []
+    let mutable remainingStrings = List.ofArray strings
+    
+    while not remainingStrings.IsEmpty do
+        let medianIndex = remainingStrings.Length / 2
+        let sortedRemaining = remainingStrings |> List.sortBy (fun s -> s.Length)
+        let medianString = sortedRemaining.[medianIndex]
+        sortedStrings <- medianString :: sortedStrings
+        remainingStrings <- remainingStrings |> List.filter (fun s -> s <> medianString)
+    
+    sortedStrings |> List.rev |> List.toArray
+
+let sortByCriteria7 (strings: string[]) =
+    strings
+    |> Array.sortBy (fun str ->
+        let chars = str.ToCharArray()
+        let mutable vcCount = 0
+        let mutable cvCount = 0
+        
+        for i in 0 .. chars.Length - 2 do
+            if isVowel chars.[i] && isConsonant chars.[i + 1] then vcCount <- vcCount + 1
+            elif isConsonant chars.[i] && isVowel chars.[i + 1] then cvCount <- cvCount + 1
+        
+        abs (vcCount - cvCount))
+
+let sortByCriteria8 (strings: string[]) =
+    strings
+    |> Array.sortBy (fun str ->
+        let chars = str.ToCharArray()
+        let avgAscii = chars |> Array.map (fun c -> float (int c)) |> Array.average
+        
+        let maxTripletAvg = 
+            if chars.Length < 3 then avgAscii
+            else
+                [| 0 .. chars.Length - 3 |]
+                |> Array.map (fun i -> 
+                    [| chars.[i]; chars.[i + 1]; chars.[i + 2] |]
+                    |> Array.map (fun c -> float (int c))
+                    |> Array.average)
+                |> Array.max
+        
+        (avgAscii - maxTripletAvg) ** 2.0)
+
+let sortByCriteria9 (strings: string[]) =
+    strings
+    |> Array.sortBy (fun str ->
+        let chars = str.ToCharArray()
+        let maxAscii = chars |> Array.map (fun c -> float (int c)) |> Array.max
+        
+        let mirrorDifferences = 
+            if chars.Length <= 1 then [| 0.0 |]
+            else
+                [| 0 .. chars.Length / 2 - 1 |]
+                |> Array.map (fun i ->
+                    let leftChar = chars.[i]
+                    let rightChar = chars.[chars.Length - 1 - i]
+                    abs (float (int leftChar) - float (int rightChar)))
+        
+        let avgMirrorDiff = if mirrorDifferences.Length > 0 then Array.average mirrorDifferences else 0.0
+        (maxAscii - avgMirrorDiff) ** 2.0)
+
+let sortByCriteria10 (strings: string[]) =
+    strings
+    |> Array.sortBy (fun str ->
+        let chars = str.ToCharArray()
+        let mutable mirrorTripletCount = 0
+        
+        for i in 0 .. chars.Length - 3 do
+            if chars.[i] = chars.[i + 2] then
+                mirrorTripletCount <- mirrorTripletCount + 1
+        
+        float mirrorTripletCount / float (max 1 (chars.Length - 2)))
+
+[<EntryPoint>]
+let main argv =
+    printfn "Задание 20: Сортировка строк по различным критериям"
+    printfn "==================================================\n"
+    
+    let testStrings = [|
+        "hello world"
+        "programming"
+        "algorithm"
+        "data structure"
+        "functional"
+        "imperative"
+        "recursion"
+        "iteration"
+        "ada"
+        "abcba"
+    |]
+    
+    printfn "Исходные строки:"
+    testStrings |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "1. Сортировка по разности между средним количеством согласных и гласных:"
+    let sorted1 = sortByCriteria1 testStrings
+    sorted1 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "2. Сортировка по среднему весу ASCII-кода символов:"
+    let sorted2 = sortByCriteria2 testStrings
+    sorted2 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "3. Сортировка по разности частоты наиболее частого символа:"
+    let sorted3 = sortByCriteria3 testStrings
+    sorted3 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "4. Сортировка по квадратичному отклонению ASCII от первой строки:"
+    let sorted4 = sortByCriteria4 testStrings
+    sorted4 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "5. Сортировка по квадратичному отклонению частоты от языковой частоты:"
+    let sorted5 = sortByCriteria5 testStrings
+    sorted5 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "6. Сортировка по медианному значению с удалением:"
+    let sorted6 = sortByCriteria6 testStrings
+    sorted6 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "7. Сортировка по разности сочетаний гласная-согласная и согласная-гласная:"
+    let sorted7 = sortByCriteria7 testStrings
+    sorted7 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "8. Сортировка по квадратичному отклонению среднего ASCII от максимального тройки:"
+    let sorted8 = sortByCriteria8 testStrings
+    sorted8 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "9. Сортировка по квадратичному отклонению максимального ASCII от зеркальных пар:"
+    let sorted9 = sortByCriteria9 testStrings
+    sorted9 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    printfn ""
+    
+    printfn "10. Сортировка по среднему количеству зеркальных троек:"
+    let sorted10 = sortByCriteria10 testStrings
+    sorted10 |> Array.iteri (fun i str -> printfn "  %d. %s" (i + 1) str)
+    
+    0
\ No newline at end of file
diff --git a/lab6/task20/task20.fsproj b/lab6/task20/task20.fsproj
new file mode 100644
index 0000000..3befcdd
--- /dev/null
+++ b/lab6/task20/task20.fsproj
@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="Program.fs" />
+  </ItemGroup>
+
+</Project>
\ No newline at end of file