diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..f8e28a2 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.Arrays;
+
 /**
  * @author leon on 01/01/2019.
  */
 public class ArrayUtils {
     public static String getMiddleElement(String[] values) {
-        return null;
+        int start = 0;
+        int end = values.length-1;
+        int mid = start + (end - start)/2;
+
+        return values[mid];
     }
 
     public static String[] removeMiddleElement(String[] values) {
-        return null;
+        String[] result = new  String[values.length-1];
+        int middle = values.length/2;
+        for(int i = 0;i < values.length; i++){
+            if(i < middle){
+                result[i] = values[i];
+            }
+            if (i > middle){
+                result[i-1] = values[i];
+            }
+        }
+        return result;
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+
+        return values[values.length-1];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+
+        return values = Arrays.copyOfRange(values,0,values.length-1);
     }
 }
\ 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..034a867 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
@@ -1,12 +1,23 @@
 package rocks.zipcode.quiz4.collections;
 
+import java.util.HashMap;
 import java.util.Map;
 
 public class WordCounter {
+    Map<String, Integer> wordCount = new HashMap<String, Integer>();
     public WordCounter(String... strings) {
-    }
 
-    public Map<String, Integer> getWordCountMap() {
-        return null;
+        for (String word : strings) {
+            if (!wordCount.containsKey(word)) {
+                wordCount.put(word, 1);
+            } else {
+                int count = wordCount.get(word);
+                wordCount.put(word, count + 1);
+            }
+        }
     }
+        public Map<String, Integer> getWordCountMap (){
+            return wordCount;
+        }
+
 }
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..00530f5 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 +1,9 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-public class Curry {
+public class Curry implements Spice{
+    private String curry = "curry";
+    @Override
+    public String getName() {
+        return curry;
+    }
 }
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..86b76a3 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 +9,36 @@
  * @author leon on 27/12/2018.
  */
 public class Food {
+    private List<Spice> spiceList;
+    private Map<Class<? extends Spice>, Integer> spiceMap;
+
+    public Food() {
+        this.spiceList = new ArrayList<>();
+        this.spiceMap = new HashMap<>();
+    }
+
     public List<Spice> getAllSpices() {
-        return null;
+        return spiceList;
     }
 
-    public <SpiceType extends Class<? extends Spice>> Map<SpiceType, Integer> getSpiceCount() {
-        return null;
+
+
+    public Map<Class<?  extends Spice>, Integer> getSpiceCount() {
+
+
+        return spiceMap;
     }
 
     public void applySpice(Spice spice) {
+        if (!spiceMap.containsKey(spice.getClass())) {
+            spiceMap.put(spice.getClass(), 1);
+        } else {
+            int numOfSpice = spiceMap.get(spice.getClass());
+            spiceMap.put(spice.getClass(), numOfSpice + 1);
+        }
+        spiceList.add(spice);
+
     }
+
+
 }
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..a0c3d28 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 +3,10 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Ginger {
+public class Ginger implements Spice{
+    private String ginger = "ginger";
+    @Override
+    public String getName() {
+        return ginger;
+    }
 }
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..a394e04 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 +3,10 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Pepper {
+public class Pepper implements Spice{
+    private String pepper = "black pepper";
+    @Override
+    public String getName() {
+        return pepper;
+    }
 }
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..6459119 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Spice.java
@@ -4,4 +4,6 @@
  * @author leon on 27/12/2018.
  */
 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..f9f5c69 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -1,35 +1,47 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import static java.lang.Math.sqrt;
+
 /**
  * @author leon on 21/12/2018.
  */
 public class Calculator {
     public static Double squareRoot(Double value) {
-        return null;
+
+        return sqrt(value);
     }
 
+
     public static Double square(Double value) {
-        return null;
+        return value * value;
     }
 
     public static Double[] squareRoots(Double... value) {
-        return null;
+        Double[] result = new  Double[value.length];
+        for(int i = 0; i < value.length; i++){
+            result[i] = Math.sqrt((value[i]));
+        }
+        return result;
     }
 
     public static Double[] squares(Double... values) {
-        return null;
+        Double[] result = new Double[values.length];
+        for(int i = 0; i < values.length; i++){
+            result[i] = Math.pow(values[i], 2);
+        }
+        return result;
     }
 
     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..3e51dea 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,67 @@
 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;
+
+        char[] arr = str.toCharArray();
+        int i = arr.length/2;
+        arr[i]= Character.toUpperCase(arr[i]);
+        String result = new String(arr);
+
+        return result;
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        char[] arr = str.toCharArray();
+        int i = arr.length/2;
+        arr[i]= Character.toLowerCase(arr[i]);
+        String result = new String(arr);
+
+        return result;
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+        //str = str.toLowerCase();
+        char arr[] = str.toCharArray();
+        Arrays.sort(arr);
+        for(int i = 0; i < str.length()-1; i++){
+            if(arr[i] == arr[i +1])
+                return false;
+        }
+        return true;
     }
 
     public static Boolean hasDuplicateConsecutiveCharacters(String str) {
-        return null;
+        return (str.matches(".*(.)\\1.*"));
     }
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
+
+
+        return str.replaceAll("(.)(\\1)+", "");
+
     }
 
     public static String invertCasing(String str) {
-        return null;
+        StringBuilder result = new StringBuilder((str.length()));
+        for (char c :  str.toCharArray()){
+            if (Character.isUpperCase(c)) {
+                c = Character.toLowerCase(c);
+            }else if(Character.isLowerCase(c)){
+                c = Character.toUpperCase(c);
+            }
+            result.append(c);
+        }
+        return result.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..02bc0ba 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 +3,23 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Account extends BankAccount {
+public class Account  {
+
+    private Long id ;
+
+    public Account() {
+    }
+
+
+
     public Long getId() {
-        return null;
+        return this.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..d962de0 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 +1,30 @@
 package rocks.zipcode.quiz4.objectorientation.account;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * @author leon on 27/12/2018.
  */
 public class Bank {
+    private List<BankAccount> accounts;
+
+    public Bank() {
+        this.accounts = new ArrayList<>();
+    }
+
     public BankAccount removeBankAccountByIndex(Integer indexNumber) {
-        return null;
+        BankAccount newAccount = accounts.get(indexNumber);
+        accounts.remove((int)indexNumber);
+        return newAccount;
     }
 
     public void addBankAccount(BankAccount bankAccount) {
+        accounts.add(bankAccount);
     }
 
     public Boolean containsBankAccount(BankAccount bankAccount) {
-        throw new UnsupportedOperationException("Method not yet implemented");
+        return accounts.contains(bankAccount);
+        //throw new UnsupportedOperationException("Method not yet implemented");
     }
 }
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..2bc8ea0 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 +3,31 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class BankAccount {
+public class BankAccount extends Account implements Transactable{
+    private  double balance;
+
     public void setBalance(Double val) {
+        this.balance = val;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) throws IllegalArgumentException {
+        if(amountToIncreaseBy < 0){
+            throw new IllegalArgumentException();
+        }
+        balance += amountToIncreaseBy;
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) throws IllegalArgumentException {
+        if(balance < amountToDecreaseBy || amountToDecreaseBy < 0){
+            throw new IllegalArgumentException();
+        }
+        balance -= amountToDecreaseBy;
+    }
+
+    @Override
+    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..15e05be 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 +3,72 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Employee {
-    public Employee() {
+public class Employee implements Worker, Transactable{
+
+    private BankAccount bankAccount;
+    private Double hoursWorked;
+    private Double wage;
+    
+
+
+
+    public Employee(){
+        bankAccount = new BankAccount();
+        hoursWorked = 0.0;
+        wage = 35.0;
     }
 
     public Employee(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+        this.wage = 35.00;
+        this.hoursWorked = 0.0;
     }
 
+
+
     public BankAccount getBankAccount() {
-        return null;
+        return bankAccount;
     }
 
     public void setBankAccount(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+        bankAccount.deposit(amountToIncreaseBy);
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        bankAccount.withdrawal(amountToDecreaseBy);
+
+    }
+
+    @Override
+    public Double getBalance() {
+        return bankAccount.getBalance();
+    }
+
+    @Override
+    public void increaseHoursWorked(Double numberOfHours) {
+        hoursWorked += numberOfHours;
+
+    }
+
+    @Override
+    public Double getHoursWorked() {
+        return this.hoursWorked;
+    }
+
+    @Override
+    public Double getHourlyWage() {
+        return wage;
+    }
 
+    @Override
+    public Double getMoneyEarned() {
+        return this.wage * this.hoursWorked;
     }
 }