diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..bbd29ad 100644
--- a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
@@ -1,22 +1,40 @@
 package rocks.zipcode.quiz4.arrays;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+
 /**
  * @author leon on 01/01/2019.
  */
 public class ArrayUtils {
     public static String getMiddleElement(String[] values) {
-        return null;
+        return values[values.length/2];
     }
 
     public static String[] removeMiddleElement(String[] values) {
-        return null;
+/*        String[] newArr = new String[values.length-1];
+        int midEl = (values.length -1) / 2  ;
+
+        for (int i = 0; i < values.length-1; i++) {
+            if(values[i] != values[midEl]){
+                newArr[i] = values[i];
+            }
+        }
+        return newArr;*/
+        ArrayList<String> result = new ArrayList<>(Arrays.asList(values));
+        result.remove(result.size()/2);
+        return result.toArray(new String[0]);
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+        return values[values.length-1];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+//        int removeThis;
+
+//        for (int i = 0; i < values.length; i++) {
+        String[] newArr = Arrays.copyOf(values, values.length-1);
+        return newArr;
     }
 }
\ No newline at end of file
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
index 02f2618..106833a 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -5,31 +5,52 @@
  */
 public class Calculator {
     public static Double squareRoot(Double value) {
-        return null;
+//        double x;
+//
+//        double squareRoot = value / 2;
+//
+//        do {
+//            x = squareRoot;
+//            squareRoot = (x + (value / x)) / 2;
+//        } while ((x - squareRoot) != 0);
+//
+//        return squareRoot;
+
+        return Math.sqrt(value);
     }
 
     public static Double square(Double value) {
-        return null;
+        return value * value;
     }
 
     public static Double[] squareRoots(Double... value) {
-        return null;
+        Double[] newArr = new Double[value.length];
+
+        for (int i = 0; i < value.length; i++) {
+            newArr[i] = Math.sqrt(value[i]);
+        }
+        return newArr;
     }
 
     public static Double[] squares(Double... values) {
-        return null;
+        Double[] newArr = new Double[values.length];
+
+        for (int i = 0; i < values.length; i++) {
+            newArr[i] = Math.pow(values[i],2);
+        }
+        return newArr;
     }
 
     public static Double add(Double value1, Double value2) {
-        return null;
+        return value1 + value2;
     }
 
     public static Double subtract(Double value1, Double value2) {
-        return null;
+        return value1 - value2;
     }
 
 
     public static Double divide(Double divisor, Double dividend) {
-        return null;
+        return divisor / dividend;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
index 5ec61be..8187f0b 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,79 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.Arrays;
+
 /**
  * @author leon on 21/12/2018.
  */
 public class StringUtils {
     public static Character getMiddleCharacter(String string) {
-        return null;
+        char[] newArr = string.toCharArray();
+        Character mid = newArr[newArr.length/2];
+        return mid;
     }
 
     public static String capitalizeMiddleCharacter(String str) {
-        return null;
+//        for (int i = 0; i < str.length(); i++) {
+//            if(str.indexOf(i) == str.indexOf(str.length()/2)){
+//                str.indexOf(i)
+//            }
+//
+//        }
+//        Character mid = str[str.length/2];
+//        Character x = getMiddleCharacter(mid);
+//        return x.toString().toUpperCase();
+        int index = str.length() / 2;
+        return str.substring(0, index) + Character.toUpperCase(getMiddleCharacter(str)) + str.substring(index + 1);
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        int index = str.length() / 2;
+        return str.substring(0, index)+ Character.toLowerCase(getMiddleCharacter(str)) + str.substring(index+1);
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+        int len = str.length();
+
+        char arr[] = str.toCharArray();
+
+        Arrays.sort(arr);
+        for (int i = 0; i < len - 1; i++) {
+            if (arr[i] == arr[i + 1])
+                return false;
+        }
+        return true;
     }
 
     public static Boolean hasDuplicateConsecutiveCharacters(String str) {
-        return null;
+        for(int i = 1; i < str.length(); i++){
+            if(str.charAt(i-1) == str.charAt(i))
+                return true;
+        }
+        return false;
     }
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
+        StringBuilder stringBuilder = new StringBuilder(str);
+        for(int i = 1; i <= str.length()-1; i++){
+            if(str.charAt(i) == str.charAt(i-1)) {
+                stringBuilder.replace(i - 1, i + 1, "");
+            }
+        }
+        return stringBuilder.toString();
     }
 
     public static String invertCasing(String str) {
-        return null;
+        char[] chars = str.toCharArray();
+
+        for (int i = 0; i < chars.length; i++) {
+            char c = chars[i];
+            if (Character.isUpperCase(c)){
+                chars[i] = Character.toLowerCase(c);
+            }
+            else if (Character.isLowerCase(c)){
+                chars[i] = Character.toUpperCase(c);
+            }
+        }
+        return new String(chars);
     }
 }
\ No newline at end of file
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
index 40eb4a8..8bfa180 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
@@ -4,10 +4,13 @@
  * @author leon on 30/12/2018.
  */
 public class Account extends BankAccount {
+    Long id;
+
     public Long getId() {
-        return null;
+        return id;
     }
 
     public void setId(Long id) {
+        this.id = id;
     }
 }