diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..8a879b7 100644
--- a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
@@ -1,22 +1,39 @@
 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;
+//        ArrayList<String> a = new ArrayList<>( Arrays.asList(values));
+//        a.remove(a.size()/2);
+//        return a.toArray(new String[0]);
+        String[] arr = new String [values.length-1];
+        for (int i = 0; i < values.length-1 ; i++) {
+            if(i<values.length/2)
+                arr[i] = values[i];
+            else
+                arr[i] = values[i+1];
+        }
+        return arr;
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+        return values[values.length-1];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+        String[] arr = new String [values.length-1];
+        for (int i = 0; i < arr.length ; i++) {
+            arr[i] = values[i];
+        }
+        return arr;
     }
 }
\ No newline at end of file
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
index 2bf5ec2..60cc5b1 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
@@ -1,12 +1,21 @@
 package rocks.zipcode.quiz4.collections;
 
+import java.util.HashMap;
 import java.util.Map;
 
 public class WordCounter {
+    Map<String, Integer> map;
     public WordCounter(String... strings) {
+        map = new HashMap<>();
+        for (String s :strings) {
+            if(map.containsKey(s))
+                map.replace(s, map.get(s)+1);
+            else
+                map.put(s,1);
+        }
     }
 
     public Map<String, Integer> getWordCountMap() {
-        return null;
+        return map;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
index 199cefc..de12542 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
@@ -1,4 +1,8 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-public class Curry {
+public class Curry implements Spice{
+    @Override
+    public String getName() {
+        return this.getClass().getSimpleName();
+    }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
index e06abbc..2fd8832 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
@@ -1,5 +1,7 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
+import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
@@ -7,14 +9,29 @@
  * @author leon on 27/12/2018.
  */
 public class Food {
+
+    Map<Class<? extends Spice>, Integer> map;
+    List<Spice> l;
+
+    public Food(){
+        map = new HashMap<>();
+        l = new ArrayList<>();
+    }
+
     public List<Spice> getAllSpices() {
-        return null;
+        return l;
     }
 
-    public <SpiceType extends Class<? extends Spice>> Map<SpiceType, Integer> getSpiceCount() {
-        return null;
+    public Map<Class<? extends Spice>, Integer> getSpiceCount() {
+        return map;
     }
 
     public void applySpice(Spice spice) {
+        l.add(spice);
+        if(map.containsKey(spice.getClass())) {
+            map.replace(spice.getClass(), map.get(spice.getClass()) + 1);
+        }else {
+            map.put(spice.getClass(), 1);
+        }
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
index 3c4e177..2690578 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
@@ -3,5 +3,9 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Ginger {
+public class Ginger implements Spice{
+    @Override
+    public String getName() {
+        return this.getClass().getSimpleName();
+    }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
index 4b771a8..be89b6b 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
@@ -3,5 +3,9 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Pepper {
+public class Pepper implements Spice{
+    @Override
+    public String getName() {
+        return this.getClass().getSimpleName();
+    }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java
index 9ab865b..a3b8edb 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java
@@ -3,5 +3,6 @@
 /**
  * @author leon on 27/12/2018.
  */
-public interface Spice {
+public interface Spice{
+    String getName();
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
index 02f2618..5291c54 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -1,35 +1,43 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.Arrays;
+
 /**
  * @author leon on 21/12/2018.
  */
 public class Calculator {
     public static Double squareRoot(Double value) {
-        return null;
+        return Math.sqrt(value);
     }
 
     public static Double square(Double value) {
-        return null;
+        return value*value;
     }
 
     public static Double[] squareRoots(Double... value) {
-        return null;
+        Double[] num = Arrays.copyOf(value,value.length );
+        for (int i = 0; i < value.length ; i++)
+            num[i] = squareRoot(num[i]);
+        return num;
     }
 
     public static Double[] squares(Double... values) {
-        return null;
+        Double[] num = Arrays.copyOf(values,values.length );
+        for (int i = 0; i < values.length ; i++)
+            num[i] = square(num[i]);
+        return num;
     }
 
     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..a991ea5 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,84 @@
 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;
+        return string.charAt(string.length()/2);
     }
 
     public static String capitalizeMiddleCharacter(String str) {
-        return null;
+        return str.substring(0,str.length()/2)
+                + Character.toUpperCase(getMiddleCharacter(str))
+                + str.substring(str.length()/2 +1, str.length());
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        return str.substring(0,str.length()/2)
+                + Character.toLowerCase(getMiddleCharacter(str))
+                + str.substring(str.length()/2 +1, str.length());
     }
 
     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;
+        char[] c = str.toCharArray();
+        char temp = c[0];
+        for (int i = 1; i < str.length(); i++) {
+            if(temp != c[i])
+                temp = c[i];
+            else
+                return true;
+        }
+        return false;
     }
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
+        char[] c = str.toCharArray();
+        char temp = c[0];
+        StringBuilder s = new StringBuilder(c[0] + "");
+        int count  = 0;
+
+        for (int i = 1; i < str.length(); i++) {
+            if(temp != c[i]) {
+                temp = c[i];
+                s.append(temp);
+                count = 0;
+            }else{
+                if(count==0){
+                    s = new StringBuilder(s.substring(0, s.length() - 1));
+                    count++;
+                }
+            }
+        }
+
+        return s.toString();
     }
 
     public static String invertCasing(String str) {
-        return null;
+        StringBuilder newStr = new StringBuilder();
+        for (char c:str.toCharArray()) {
+            if(Character.isUpperCase(c))
+                newStr.append(Character.toLowerCase(c));
+            else if (Character.isLowerCase(c))
+                newStr.append(Character.toUpperCase(c));
+            else
+                newStr.append(c);
+        }
+        return newStr.toString();
     }
 }
\ 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..882a478 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
@@ -3,11 +3,15 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Account extends BankAccount {
+public class Account{
+
+    Long id;
+
     public Long getId() {
-        return null;
+        return id;
     }
 
     public void setId(Long id) {
+        this.id = id;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
index 0dd4183..3de91e5 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
@@ -1,17 +1,24 @@
 package rocks.zipcode.quiz4.objectorientation.account;
 
+import java.util.ArrayList;
+
 /**
  * @author leon on 27/12/2018.
  */
 public class Bank {
+    ArrayList<BankAccount> list = new ArrayList<>();
+
     public BankAccount removeBankAccountByIndex(Integer indexNumber) {
-        return null;
+        int i = indexNumber;
+        return list.remove(i);
     }
 
     public void addBankAccount(BankAccount bankAccount) {
+        list.add(bankAccount);
     }
 
     public Boolean containsBankAccount(BankAccount bankAccount) {
-        throw new UnsupportedOperationException("Method not yet implemented");
+        //throw new UnsupportedOperationException("Method not yet implemented");
+        return list.contains(bankAccount);
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
index 70ccb74..5e704b3 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
@@ -3,7 +3,34 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class BankAccount {
+public class BankAccount extends Account implements Transactable {
+    Double balance;
+
+
+    public BankAccount(){
+        balance = 0.0;
+    }
     public void setBalance(Double val) {
+        balance = val;
     }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+        if(amountToIncreaseBy < 0 )
+            throw new IllegalArgumentException();
+        balance += amountToIncreaseBy;
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        if(amountToDecreaseBy < 0 || balance - amountToDecreaseBy<0 )
+            throw new IllegalArgumentException();
+
+        balance -= amountToDecreaseBy;
+    }
+
+    public Double getBalance() {
+        return balance;
+    }
+
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
index 8407f1a..1d445ee 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
@@ -3,18 +3,61 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Employee {
+public class Employee implements Worker, Transactable {
+    BankAccount bankAccount;
+    Double hoursWorked;
+    Double hourlyWage;
+
     public Employee() {
+        this(new BankAccount());
     }
 
     public Employee(BankAccount bankAccount) {
+        hourlyWage = 35.0;
+        hoursWorked = 0.0;
+        this.bankAccount = bankAccount;
     }
 
     public BankAccount getBankAccount() {
-        return null;
+        return bankAccount;
     }
 
     public void setBankAccount(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+    }
+
+    @Override
+    public void increaseHoursWorked(Double numberOfHours) {
+        hoursWorked += numberOfHours;
+    }
+
+    @Override
+    public Double getHoursWorked() {
+        return hoursWorked;
+    }
+
+    @Override
+    public Double getHourlyWage() {
+        return hourlyWage;
+    }
+
+    @Override
+    public Double getMoneyEarned() {
+        return hourlyWage*hoursWorked;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+        bankAccount.setBalance( bankAccount.getBalance() + amountToIncreaseBy);
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        bankAccount.setBalance( bankAccount.getBalance() - amountToDecreaseBy);
+    }
 
+    @Override
+    public Double getBalance() {
+        return bankAccount.getBalance();
     }
 }