diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..d1b995a 100644
--- a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
@@ -1,22 +1,38 @@
 package rocks.zipcode.quiz4.arrays;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * @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;
+
+        List<String> temp = new ArrayList<>();
+        String[] result = new String[0];
+
+        for (int i = 0; i < values.length; i++){
+            if (i != values.length/2) temp.add(values[i]);
+        }
+        return temp.toArray(result);
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+
+        return values[values.length-1];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+        String [] result = new String[values.length-1];
+
+        for (int i = 0; i < result.length; i++){
+            result[i] = values[i];
+        }
+        return result;
     }
 }
\ 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..1bddc0b 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
@@ -1,12 +1,29 @@
 package rocks.zipcode.quiz4.collections;
 
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 
 public class WordCounter {
+
+    Map<String,Integer> words = new HashMap<>();
+    Integer counter;
+
     public WordCounter(String... strings) {
+
+        for (String each : strings){
+            counter = words.get(each);
+            if (counter == null){
+                counter = 1;
+            } else counter ++;
+
+            words.put(each,counter);
+        }
+
     }
 
     public Map<String, Integer> getWordCountMap() {
-        return null;
+        return words;
     }
 }
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..c6b96b4 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 +1,4 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-public class Curry {
+public class Curry implements Spice {
 }
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..09ba6d0 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 +9,26 @@
  * @author leon on 27/12/2018.
  */
 public class Food {
+
+    List<Spice> allSpices = new ArrayList<>();
+
     public List<Spice> getAllSpices() {
-        return null;
+
+        return allSpices;
     }
 
     public <SpiceType extends Class<? extends Spice>> Map<SpiceType, Integer> getSpiceCount() {
-        return null;
+
+        Map<SpiceType, Integer> spiceCountMap = new HashMap<>();
+
+        SpiceType spice = (SpiceType)this.allSpices.get(0).getClass();
+        Integer spiceCount = this.allSpices.size();
+
+        spiceCountMap.put(spice,spiceCount);
+        return spiceCountMap;
     }
 
     public void applySpice(Spice spice) {
+        allSpices.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..ef695be 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 +3,5 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Ginger {
+public class Ginger implements Spice{
 }
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..248859f 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 +3,5 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Pepper {
+public class Pepper implements Spice{
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
index 02f2618..395274c 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -1,35 +1,58 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.ArrayList;
+import java.util.List;
+
 /**
  * @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;
+        List<Double> array = new ArrayList<>();
+        Double[] result = new Double[0];
+
+        for(Double each : value){
+            array.add(Math.sqrt(each));
+        }
+        return array.toArray(result);
     }
 
     public static Double[] squares(Double... values) {
-        return null;
+        List<Double> array = new ArrayList<>();
+        Double[] result = new Double[0];
+
+        for(Double each : values){
+            array.add(each * each);
+        }
+        return array.toArray(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;
+
+        if (dividend == 0){
+            return 0.0;
+        }
+        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..6c2a0bb 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,102 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.*;
+
 /**
  * @author leon on 21/12/2018.
  */
 public class StringUtils {
+
     public static Character getMiddleCharacter(String string) {
-        return null;
+        int middle = string.length() / 2;
+        return string.charAt(middle);
     }
 
     public static String capitalizeMiddleCharacter(String str) {
-        return null;
+        String result = "";
+
+        for (int i = 0; i < str.length(); i++) {
+            if (i == str.length() / 2) {
+                result = result.concat(String.valueOf(str.toUpperCase().charAt(i)));
+            } else {
+                result = result.concat(String.valueOf(str.charAt(i)));
+            }
+        }
+
+        return result;
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        String result = "";
+
+        for (int i = 0; i < str.length(); i++) {
+            if (i == str.length() / 2) {
+                result = result.concat(String.valueOf(str.toLowerCase().charAt(i)));
+            } else {
+                result = result.concat(String.valueOf(str.charAt(i)));
+            }
+        }
+
+        return result;
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+
+        Set<Character> unique = new HashSet<>();
+        for (Character c : str.toCharArray()) {
+            unique.add(c);
+        }
+        if (unique.size() == str.length()) {
+            return true;
+        } else {
+            return false;
+        }
     }
 
     public static Boolean hasDuplicateConsecutiveCharacters(String str) {
-        return null;
+
+        for (int i = 0; i < str.length() - 1; i++) {
+            if (str.charAt(i) == str.charAt(i + 1))
+                return true;
+        }
+        return false;
     }
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
+        String result = str;
+
+        for (int i = 0; i < str.length() - 1; i++){
+            if (str.charAt(i) == str.charAt(i+1)){
+                result = removedChars(result,str.charAt(i));
+            }
+        }
+        return result;
+    }
+
+    private static String removedChars(String str, Character charToRemove){
+        String result = str;
+
+        result = result.replace(charToRemove.toString(), "");
+
+        return result;
     }
 
     public static String invertCasing(String str) {
-        return null;
+        String[] temp = str.split("");
+        String result = "";
+
+        for (int i = 0; i < temp.length; i++) {
+            if (temp[i].toUpperCase().equals(temp[i])) {
+                temp[i] = temp[i].toLowerCase();
+                result = result.concat(temp[i]);
+            } else if (temp[i].toLowerCase().equals(temp[i])) {
+                temp[i] = temp[i].toUpperCase();
+                result = result.concat(temp[i]);
+            } else {
+                result = result.concat(temp[i]);
+            }
+        }
+
+        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..f2e7b46 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 {
+    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..7eff5ff 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 {
-    public BankAccount removeBankAccountByIndex(Integer indexNumber) {
-        return null;
+
+    List<BankAccount> bankAccounts = new ArrayList<>();
+
+    public boolean removeBankAccountByIndex(Integer indexNumber) {
+        BankAccount temp = null;
+
+        if (bankAccounts.size() > 0 && indexNumber <= bankAccounts.size()){
+            temp = bankAccounts.get(indexNumber);
+            bankAccounts.remove(temp);
+        }
+        return containsBankAccount(temp);
     }
 
     public void addBankAccount(BankAccount bankAccount) {
+        bankAccounts.add(bankAccount);
     }
 
     public Boolean containsBankAccount(BankAccount bankAccount) {
-        throw new UnsupportedOperationException("Method not yet implemented");
+        return bankAccounts.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..760d602 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
@@ -1,9 +1,39 @@
 package rocks.zipcode.quiz4.objectorientation.account;
 
+import static java.lang.Math.abs;
+
 /**
  * @author leon on 27/12/2018.
  */
-public class BankAccount {
+public class BankAccount extends Account implements Transactable{
+
+    Double accountBalance;
+
+    public BankAccount(){
+        this.accountBalance = 0.0;
+    }
+
     public void setBalance(Double val) {
+        this.accountBalance =val;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+        if (amountToIncreaseBy < 0) throw  new IllegalArgumentException();
+
+        accountBalance += amountToIncreaseBy;
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        if (abs(amountToDecreaseBy) > this.accountBalance || this.accountBalance == 0){
+            throw new IllegalArgumentException();
+        }
+        accountBalance -= amountToDecreaseBy;
+    }
+
+    @Override
+    public Double getBalance() {
+        return this.accountBalance;
     }
 }
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..5bae4f7 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 +3,70 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Employee {
+public class Employee implements Worker,Transactable {
+
+    private BankAccount bankAccount;
+    private Double hoursWorked;
+    private Double hourlyWage;
+
     public Employee() {
+        this.hourlyWage = 35.0;
+        this.hoursWorked = 0.0;
+        this.bankAccount = new BankAccount();
     }
 
     public Employee(BankAccount bankAccount) {
+        this.hourlyWage = 35.0;
+        this.hoursWorked = 0.0;
+        this.bankAccount = bankAccount;
     }
 
     public BankAccount getBankAccount() {
-        return null;
+
+        return this.bankAccount;
     }
 
     public void setBankAccount(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+
+        if (amountToIncreaseBy > 0) {
+            this.bankAccount.deposit(amountToIncreaseBy);
+        }
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        this.bankAccount.withdrawal(amountToDecreaseBy);
+    }
+
+    @Override
+    public Double getBalance() {
+        return this.bankAccount.getBalance();
+    }
+
+    @Override
+    public void increaseHoursWorked(Double numberOfHours) {
+        if (numberOfHours > 0){
+            this.hoursWorked = this.hoursWorked + numberOfHours;
+        }
+    }
+
+    @Override
+    public Double getHoursWorked() {
+        return this.hoursWorked;
+    }
+
+    @Override
+    public Double getHourlyWage() {
+        return this.hourlyWage;
+    }
 
+    @Override
+    public Double getMoneyEarned() {
+        return this.hourlyWage * this.hoursWorked;
     }
 }