diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..8eccc2c 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 rocks.zipcode.quiz4.fundamentals.StringUtils;
+
+import java.lang.reflect.Array;
+import java.util.*;
+
 /**
  * @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> list = new ArrayList<>(Arrays.asList(values));
+        list.remove(list.size()/2);
+       return listToStringArr(list);
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+        return values[values.length-1];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+        Deque<String> list = new ArrayDeque<>(Arrays.asList(values));
+        list.removeLast();
+        String[] result = new String[list.size()];
+        result = list.toArray(result);
+        return result;
     }
+
+    public static String[] listToStringArr(List<String> list){
+        String[] result = new String[list.size()];
+        result = list.toArray(result);
+        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..7248166 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
@@ -1,12 +1,30 @@
 package rocks.zipcode.quiz4.collections;
 
-import java.util.Map;
+import java.util.*;
+import java.util.stream.Collectors;
 
 public class WordCounter {
+    private Map<String, Integer> wordsMap;
+    private List<String> wordsList;
+
     public WordCounter(String... strings) {
+        wordsMap = new HashMap<>();
+        wordsList = Arrays
+                .stream(strings)
+                .collect(Collectors.toCollection(ArrayList::new));
+
     }
 
     public Map<String, Integer> getWordCountMap() {
-        return null;
+        for(String s : wordsList){
+            if(!wordsMap.containsKey(s)){
+                wordsMap.put(s,1);
+            }
+            else{
+                int count = wordsMap.get(s);
+                wordsMap.put(s, count+1);
+            }
+        }
+        return wordsMap;
     }
 }
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..421c97a 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 +1,11 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-public class Curry {
+public class Curry implements Spice{
+
+
+    @Override
+    public String getName() {
+
+        return this.getClass().toString();
+    }
 }
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..51c2051 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
@@ -1,20 +1,43 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
+import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.stream.Collectors;
 
 /**
  * @author leon on 27/12/2018.
  */
 public class Food {
+    private List<Spice> spices;
+
+
+    public Food(){
+        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> spiceMap = new HashMap<>();
+        spices.forEach(s -> spiceMap.compute((SpiceType) s.getClass(), (k, v) -> (v == null) ? 1 : v + 1));
+        return spiceMap;
     }
 
+
+
     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..e7ec910 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 +3,12 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Ginger {
+public class Ginger implements Spice{
+
+
+    @Override
+    public String getName() {
+
+        return this.getClass().toString();
+    }
 }
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..cb951e4 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 +3,12 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Pepper {
+public class Pepper implements Spice{
+
+
+
+    @Override
+    public String getName() {
+        return this.getClass().toString();
+    }
 }
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..e73857c 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 {
+    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..d0cd5c3 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -1,35 +1,60 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.lang.reflect.Array;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
 /**
  * @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> list = Arrays
+                .stream(value)
+                .map(Math::sqrt)
+                .collect(Collectors.toCollection(ArrayList::new));
+        Double[] result = new Double[list.size()];
+         result = list.toArray(result);
+         return result;
     }
 
     public static Double[] squares(Double... values) {
-        return null;
+        List<Double> list = Arrays
+                .stream(values)
+                .map(d->d*d)
+                .collect(Collectors.toCollection(ArrayList::new));
+        Double[] result = new Double[list.size()];
+        result = list.toArray(result);
+        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..5fe7d43 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,71 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+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;
+        StringBuilder sb = new StringBuilder(str);
+        sb.setCharAt(str.length()/2, Character.toUpperCase(getMiddleCharacter(str)));
+        return sb.toString();
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        StringBuilder sb = new StringBuilder(str);
+        sb.setCharAt(str.length()/2, Character.toLowerCase(getMiddleCharacter(str)));
+        return sb.toString();
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+        return stringToCharList(str).stream().allMatch(new HashSet<>()::add);
     }
 
     public static Boolean hasDuplicateConsecutiveCharacters(String str) {
-        return null;
+        return (str.matches(".*(.)\\1.*"));
     }
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
+        StringBuilder sb = new StringBuilder(str);
+            int count = 0;
+            while (count < sb.length() -1){
+                if(sb.charAt(count) == sb.charAt(count+1)){
+                    sb.deleteCharAt(count);
+                    sb.deleteCharAt(count);
+                }
+                count+=1;
+            }
+           return sb.toString();
+
     }
 
     public static String invertCasing(String str) {
-        return null;
+        StringBuilder sb = new StringBuilder();
+        for (Character c : stringToCharList(str)){
+            if(Character.toUpperCase(c) == c){
+                c = Character.toLowerCase(c);
+            }
+            else {
+                c = Character.toUpperCase(c);
+            }
+            sb.append(c);
+        }
+        return sb.toString();
     }
+
+    public static List<Character> stringToCharList(String s){
+        return s.chars().mapToObj((i) -> (char) i).collect(Collectors.toList());
+    }
+
 }
\ 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..e7e642f 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 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..4732427 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 +1,28 @@
 package rocks.zipcode.quiz4.objectorientation.account;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
 /**
  * @author leon on 27/12/2018.
  */
 public class Bank {
+    private List<BankAccount> accounts = new ArrayList<>();
+
     public BankAccount removeBankAccountByIndex(Integer indexNumber) {
-        return null;
+        BankAccount toBeRemoved = accounts.get(indexNumber);
+       accounts = accounts.stream().filter(a -> a != toBeRemoved).collect(Collectors.toList());
+        return toBeRemoved;
     }
 
     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..c0af1a8 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 +3,42 @@
 /**
  * @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){
+                    this.balance+=amountToIncreaseBy;
+                }
+                else {
+                    throw new IllegalArgumentException();
+                }
+
+        }
+
+
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+        if(balance - amountToDecreaseBy >= 0 && amountToDecreaseBy > 0){
+            balance-=amountToDecreaseBy;
+        }
+        else {
+            throw new IllegalArgumentException();
+        }
+    }
+
+    @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..7ff95d0 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 +3,77 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Employee {
+public class Employee implements Worker, Transactable{
+   private Double hourlyWage;
+   private Double hoursWorked;
+   private BankAccount account;
+
     public Employee() {
+        hourlyWage = 35.0;
+        hoursWorked = 0.0;
+        account = new BankAccount();
     }
 
     public Employee(BankAccount bankAccount) {
+        hourlyWage = 35.0;
+        hoursWorked = 0.0;
+        account = bankAccount;
     }
 
     public BankAccount getBankAccount() {
-        return null;
+        return account;
     }
 
     public void setBankAccount(BankAccount bankAccount) {
+        account = bankAccount;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) {
+        account.setBalance(account.getBalance()+amountToIncreaseBy);
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) {
+
+    }
+
+    @Override
+    public Double getBalance() {
+        return account.getBalance();
+    }
+
+    @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;
+    }
+
+    public static void main(String[] args) {
+        Employee employee = new Employee();
+
+        // and employee is a `Worker`
+        Worker workerEmployee = employee;
+
+        // and employee is a `Transactable`
+        Transactable transactableEmployee = employee;
 
+        // and `BankAccount` is `Transactable`
+        Transactable bankAccount = employee.getBankAccount();
+        System.out.println(bankAccount.getBalance());
     }
 }
diff --git a/src/test/java/rocks/zipcode/quiz4/objectorientation/employee/EmployeeConstructorTest.java b/src/test/java/rocks/zipcode/quiz4/objectorientation/employee/EmployeeConstructorTest.java
index 67787a4..4e9e05e 100644
--- a/src/test/java/rocks/zipcode/quiz4/objectorientation/employee/EmployeeConstructorTest.java
+++ b/src/test/java/rocks/zipcode/quiz4/objectorientation/employee/EmployeeConstructorTest.java
@@ -73,6 +73,7 @@ public void testNonNullaryConstructor() {
 
         // then
         Assert.assertNotNull(employee.getBankAccount());
+        System.out.println(employee.getHourlyWage());
         Assert.assertEquals(expectedHourlyWage, workerEmployee.getHourlyWage());
         Assert.assertEquals(expectedHoursWorked, workerEmployee.getHoursWorked());
         Assert.assertEquals(expectedBalance, transactableEmployee.getBalance());