diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..7b54e65 100644
--- a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
@@ -1,22 +1,37 @@
 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> newArr = new ArrayList<>(Arrays.asList(values));
+        newArr.remove(getMiddleElement(values));
+        values = new String[newArr.size()];
+        newArr.toArray(values);
+        return values;
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+
+        return values[values.length - 1];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+//        ArrayList<String> newArr = new ArrayList<>(Arrays.asList(values));
+//        newArr.remove(getLastElement(values));
+//        values = new String[newArr.size()];
+//        newArr.toArray(values);
+//        return values;
+
+        return 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..a1431d9 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
@@ -1,12 +1,24 @@
 package rocks.zipcode.quiz4.collections;
 
+import java.util.HashMap;
 import java.util.Map;
 
 public class WordCounter {
+
+    private HashMap<String, Integer> wordCount = new HashMap<>();
+
     public WordCounter(String... strings) {
+        for(String str : strings){
+            if(!this.wordCount.keySet().contains(str)){
+                this.wordCount.put(str, 1);
+            }
+            else {
+                this.wordCount.replace(str, this.wordCount.get(str) + 1);
+            }
+        }
     }
 
     public Map<String, Integer> getWordCountMap() {
-        return null;
+        return this.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..0649b71 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 +1,21 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-public class Curry {
+public class Curry implements Spice{
+    String name;
+
+    public Curry() {
+        this.name = null;
+    }
+
+    public Curry(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
 }
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..607b210 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 +9,31 @@
  * @author leon on 27/12/2018.
  */
 public class Food {
+
+    List<Spice> spices;
+
+    public Food() {
+        this.spices = new ArrayList<>();
+    }
+
     public List<Spice> getAllSpices() {
-        return null;
+        return spices;
     }
 
     public <SpiceType extends Class<? extends Spice>> Map<SpiceType, Integer> getSpiceCount() {
-        return null;
+        Map<SpiceType, Integer> spiceCountMap = new HashMap<>();
+        for (Spice spice : spices) {
+            SpiceType type = (SpiceType) spice.getClass();
+            if(spiceCountMap.putIfAbsent(type, 1) != null) {
+                Integer count = spiceCountMap.get(type) + 1;
+                spiceCountMap.replace(type, count);
+            }
+        }
+        return spiceCountMap;
     }
 
     public void applySpice(Spice spice) {
+        spices.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..49b4f18 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 +3,22 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Ginger {
+public class Ginger implements Spice{
+    String name;
+
+    public Ginger() {
+        this.name = null;
+    }
+
+    public Ginger(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
 }
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..372bf1d 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 +3,22 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Pepper {
+public class Pepper implements Spice{
+    String name;
+
+    public Pepper() {
+        this.name = null;
+    }
+
+    public Pepper(String name) {
+        this.name = name;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
index 02f2618..598eebd 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -5,31 +5,40 @@
  */
 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[] sqArr = new Double[value.length];
+        for(int i = 0; i < value.length; i++){
+            sqArr[i] = Math.sqrt(value[i]);
+        }
+        return sqArr;
     }
 
     public static Double[] squares(Double... values) {
-        return null;
+        Double[] sqArr = new Double[values.length];
+        for(int i = 0; i < values.length; i++){
+            sqArr[i] = (values[i] * values[i]);
+        }
+        return sqArr;
     }
 
     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..d2b142b 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,77 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.ArrayList;
+
 /**
  * @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;
+        Integer middle = str.length()/2;
+        return str.substring(0,middle) +
+                str.substring(middle, middle+1).toUpperCase() +
+                str.substring(middle+1);
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        Integer middle = str.length()/2;
+        return str.substring(0,middle) +
+                str.substring(middle, middle+1).toLowerCase() +
+                str.substring(middle+1);
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+        for(int i = 0; i < str.length()-1; i++){
+            for(int j = i+1; j < str.length(); j++){
+                if (str.charAt(i) == str.charAt(j))
+                    return false;
+            }
+        }
+        return true;
     }
 
     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;
+        ArrayList<String> removed = new ArrayList<>();
+        for (int i = 0; i < str.length() - 1; i++) {
+            if(str.charAt(i) == str.charAt(i+1)) {
+                String remove = str.substring(i, i+2);
+                removed.add(remove);
+            }
+        }
+
+        String newString = str;
+        for (String s: removed) {
+            newString = newString.replace(s, "");
+        }
+
+        return newString;
     }
 
     public static String invertCasing(String str) {
-        return null;
+        StringBuilder newStr = new StringBuilder();
+        for (int i = 0; i < str.length(); i++) {
+            if(Character.isUpperCase(str.charAt(i))) {
+                newStr.append(Character.toLowerCase(str.charAt(i)));
+            } else if(Character.isLowerCase(str.charAt(i))) {
+                newStr.append(Character.toUpperCase(str.charAt(i)));
+            } else {
+                newStr.append(str.charAt(i));
+            }
+        }
+
+        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..519d168 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..b58239a 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 +1,29 @@
 package rocks.zipcode.quiz4.objectorientation.account;
 
+import java.util.ArrayList;
+
 /**
  * @author leon on 27/12/2018.
  */
 public class Bank {
+    ArrayList<BankAccount> accountList;
+
+    public Bank(){
+        this.accountList = new ArrayList<BankAccount>();
+    }
+
     public BankAccount removeBankAccountByIndex(Integer indexNumber) {
-        return null;
+        BankAccount removed = accountList.get(indexNumber);
+        accountList.remove((int) indexNumber);
+        return removed;
     }
 
     public void addBankAccount(BankAccount bankAccount) {
+        accountList.add(bankAccount);
     }
 
     public Boolean containsBankAccount(BankAccount bankAccount) {
-        throw new UnsupportedOperationException("Method not yet implemented");
+        return accountList.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..6e1283e 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 +3,32 @@
 /**
  * @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;
+    }
+
+    public BankAccount(){
+        this.balance = 0.00;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+        if (amountToIncreaseBy >= 0) setBalance(getBalance() + amountToIncreaseBy);
+        else throw new IllegalArgumentException();
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        if (amountToDecreaseBy < 0 || amountToDecreaseBy > getBalance()) throw new IllegalArgumentException();
+        setBalance(getBalance() - amountToDecreaseBy);
+    }
+
+    @Override
+    public Double getBalance() {
+        return this.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..b69fb45 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 +3,63 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Employee {
+public class Employee implements Transactable, Worker{
+    BankAccount bankAccount;
+    Double hoursWorked;
+    Double hourlyWage;
+
     public Employee() {
+        bankAccount = new BankAccount();
+        hourlyWage = 35.0;
+        hoursWorked = 0.0;
     }
 
     public Employee(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+        hourlyWage = 35.0;
+        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 = hoursWorked + numberOfHours;
+    }
+
+    @Override
+    public Double getHoursWorked() {
+        return hoursWorked;
+    }
+
+    @Override
+    public Double getHourlyWage() {
+        return hourlyWage;
+    }
 
+    @Override
+    public Double getMoneyEarned() {
+        return hourlyWage * hoursWorked;
     }
 }