diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..89cb70f 100644
--- a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
@@ -1,22 +1,53 @@
 package rocks.zipcode.quiz4.arrays;
 
+import java.util.stream.Stream;
+
 /**
  * @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[] removeMiddle = new String[values.length - 1];
+//        int mid = values.length / 2;
+//        for (int i = 0; i < values.length ; i++) {
+//            if(i < mid){
+//                removeMiddle[i] = values[i];
+//            }
+//            if(i > mid) {
+//                removeMiddle[i-1] = values[i];
+//            }
+//        }
+//
+//        return removeMiddle;
+        return Stream.of(values)
+                .filter(v -> !v.equals(getMiddleElement(values)))
+                .toArray(String[]::new);
+
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+        return values[values.length - 1];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+        String[] removeLast = new String[values.length-1];
+        System.arraycopy(values, 0, removeLast, 0, values.length - 1);
+        return removeLast;
     }
+
+    //    arraycopy(Object source_arr, int sourcePos,
+//              Object dest_arr, int destPos, int len)
+//    Parameters :
+//    source_arr : array to be copied from
+//    sourcePos : starting position in source array from where to copy
+//    dest_arr : array to be copied in
+//    destPos : starting position in destination array, where to copy in
+//    len : total no. of components to be copied.
+
 }
\ 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..3068634 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
@@ -1,12 +1,32 @@
 package rocks.zipcode.quiz4.collections;
 
+import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
 
 public class WordCounter {
+
+    String[] stringArray;
+
     public WordCounter(String... strings) {
+        this.stringArray = strings;
     }
 
     public Map<String, Integer> getWordCountMap() {
-        return null;
+
+        Map<String, Integer> map = new HashMap<>();
+//
+//        for(String s : stringArray){
+//            if(map.keySet().contains(s)){
+//                map.put(s, map.get(s)+1);
+//            } else {
+//                map.put(s,1);
+//            }
+//        }
+        for(String s : stringArray){
+            map.compute(s, (k,v) -> (v == null) ? 1 : v+1);
+        }
+        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..c4abe9b 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 +1,10 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-public class Curry {
+public class Curry implements Spice{
+
+    @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..fecb8a6 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> spicesAdded;
+
     public List<Spice> getAllSpices() {
-        return null;
+        return spicesAdded;
+    }
+
+    public Food() {
+        this.spicesAdded = new ArrayList<>();
     }
 
     public <SpiceType extends Class<? extends Spice>> Map<SpiceType, Integer> getSpiceCount() {
-        return null;
+        Map<SpiceType, Integer> map = new HashMap<>();
+//        for (Spice s: spicesAdded) {
+//            SpiceType spice = (SpiceType)s.getClass();
+//            if(map.containsKey(spice)){
+//                map.replace(spice, map.get(spice),map.get(spice) +1);
+//            }else {
+//                map.put(spice,1);
+//            }
+//        }
+//        return map;
+        for(Spice s: spicesAdded){
+            map.compute((SpiceType)s.getClass(), (k,v) -> (v == null) ? 1: v+1);
+        }
+        return map;
     }
 
     public void applySpice(Spice spice) {
+        spicesAdded.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..17b0fb8 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{
+    @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..97cd24f 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{
+    @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..ed6e324 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 +4,5 @@
  * @author leon on 27/12/2018.
  */
 public interface Spice {
+    public 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..154373c 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -1,35 +1,35 @@
 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;
+        return Arrays.stream(value).map(Calculator::squareRoot).toArray(Double[]::new);
     }
 
     public static Double[] squares(Double... values) {
-        return null;
+        return Arrays.stream(values).map(Calculator::square).toArray(Double[]::new);
     }
 
-    public static Double add(Double value1, Double value2) {
-        return null;
-    }
+    public static Double add(Double value1, Double value2) { 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..c9a3366 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,70 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Stream;
+
 /**
  * @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;
+        int middle = str.length() / 2;
+        return str.substring(0,middle)+ Character.toUpperCase(getMiddleCharacter(str)) + str.substring(middle + 1);
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        int middle = str.length() / 2;
+        return str.substring(0,middle)+ Character.toLowerCase(getMiddleCharacter(str)) + str.substring(middle + 1);
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+        Set result = new HashSet();
+        for (int i = 0; i < str.length(); i++) {
+            result.add(str.charAt(i));
+        }
+        return str.length() == result.size();
     }
 
     public static Boolean hasDuplicateConsecutiveCharacters(String str) {
-        return null;
+        for (int i = 1; i < str.length() ; i++) {
+            if(str.charAt(i) == str.charAt(i-1)){
+                return true;
+            }
+        }
+        return false;
     }
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
+
+        String result = "";
+        int index = 0;
+        for (int i = 1; i < str.length() ; i++) {
+            if(str.charAt(i) == str.charAt(i-1)){
+                result += str.substring(index, i-1);
+                index = 1 + i;
+            }
+        }
+        result += str.substring(index);
+        return result;
+
     }
 
     public static String invertCasing(String str) {
-        return null;
+        String[] arr = str.split("");
+        String result = "";
+        for (String s : arr){
+            if(Character.isUpperCase(s.charAt(0))){
+                result += s.toLowerCase();
+            } else{
+               result += s.toUpperCase();
+            }
+        }
+        return result;
     }
+
 }
\ 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..3e2789a 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 +3,16 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Account extends BankAccount {
+public class Account  {
+
+    private long id;
+
     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..6c3d9cb 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 account = accounts.get(indexNumber);
+        accounts.remove((int)indexNumber);
+        return account;
     }
 
     public void addBankAccount(BankAccount bankAccount) {
+        accounts.add(bankAccount);
     }
 
     public Boolean containsBankAccount(BankAccount bankAccount) {
-        throw new UnsupportedOperationException("Method not yet implemented");
+        return accounts.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..16fdf25 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 +3,40 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class BankAccount {
+public class BankAccount extends Account implements Transactable {
+
+    private double balance;
+
+    public BankAccount(){
+        balance = 0.0;
+    }
+
     public void setBalance(Double val) {
+        this.balance = val;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+        if(amountToIncreaseBy < 0) {
+            throw new IllegalArgumentException("Can't deposit negative money");
+        }
+        balance += amountToIncreaseBy;
     }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        if(amountToDecreaseBy < 0){
+            throw new IllegalArgumentException("Can't withdraw a negative amount");
+        }else if(amountToDecreaseBy > balance){
+            throw new IllegalArgumentException("Balance is too low!");
+        } else {
+            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..4c1c4ab 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 +3,65 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class 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;
+        hoursWorked = 0.0;
+        wage = 35.0;
     }
 
     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;
     }
 }
diff --git a/src/test/java/rocks/zipcode/quiz4/objectorientation/employee/EmployeePolymorphismTest.java b/src/test/java/rocks/zipcode/quiz4/objectorientation/employee/EmployeePolymorphismTest.java
index ffc4422..fd37e08 100644
--- a/src/test/java/rocks/zipcode/quiz4/objectorientation/employee/EmployeePolymorphismTest.java
+++ b/src/test/java/rocks/zipcode/quiz4/objectorientation/employee/EmployeePolymorphismTest.java
@@ -22,7 +22,7 @@ public void test1() {
     public void test2() {
         Assert.assertTrue(employee instanceof Worker);
     }
-
+    @Test
     public void test3() {
         Assert.assertFalse(employee instanceof Account);
     }