diff --git a/extra/1-currency-conversion.js b/extra/1-currency-conversion.js
index 75b3c6aab..ed7bdaf6c 100644
--- a/extra/1-currency-conversion.js
+++ b/extra/1-currency-conversion.js
@@ -5,7 +5,9 @@
   Write a function that converts a price to USD (exchange rate is 1.4 $ to £)
 */
 
-function convertToUSD() {}
+function convertToUSD(amount) {
+  return amount * 1.4;
+}
 
 /*
   CURRENCY CONVERSION
@@ -15,7 +17,9 @@ function convertToUSD() {}
   They have also decided that they should add a 1% fee to all foreign transactions, which means you only convert 99% of the £ to BRL.
 */
 
-function convertToBRL() {}
+function convertToBRL(amount) {
+  return parseFloat((amount * 0.99 * 5.7).toFixed(2));
+}
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/extra/2-piping.js b/extra/2-piping.js
index b4f8c4c1b..17261d4b4 100644
--- a/extra/2-piping.js
+++ b/extra/2-piping.js
@@ -16,26 +16,29 @@
   the final result to the variable goodCode
 */
 
-function add() {
-
+function add(a, b) {
+  return a + b;
 }
 
-function multiply() {
-
+function multiply(a, b) {
+  return a * b;
 }
 
-function format() {
+function format(digit) {
+  return `£${digit.toString()}`;
 
 }
 
 const startingValue = 2;
 
 // Why can this code be seen as bad practice? Comment your answer.
-let badCode =
+let badCode = format((startingValue + 10) * 2);  
+
+// functions are not really used, so it would work just for one case
 
 /* BETTER PRACTICE */
 
-let goodCode =
+let goodCode = format(multiply(add(startingValue, 10), 2));
 
 /* ======= TESTS - DO NOT MODIFY ===== 
 There are some Tests in this file that will help you work out if your code is working.
diff --git a/extra/3-magic-8-ball.js b/extra/3-magic-8-ball.js
index 46f65f928..923e3d30b 100644
--- a/extra/3-magic-8-ball.js
+++ b/extra/3-magic-8-ball.js
@@ -1,53 +1,70 @@
-/**
-
-  Let's peer into the future using a Magic 8 Ball!
-  https://en.wikipedia.org/wiki/Magic_8-Ball 
-
-  There are a few steps to being able view the future though:
-  * Ask a question
-  * Shake the ball
-  * Get an answer
-  * Decide if it's positive or negative
-
-  The question can be anything, but the answers are fixed,
-  and have different levels of positivity or negativity.
-
-  Below are the possible answers:
-
-  ## Very positive
-    It is certain.
-    It is decidedly so.
-    Without a doubt.
-    Yes - definitely.
-    You may rely on it.
-
-  ## Positive
-    As I see it, yes.
-    Most likely.
-    Outlook good.
-    Yes.
-    Signs point to yes.
-
-  ## Negative
-    Reply hazy, try again.
-    Ask again later.
-    Better not tell you now.
-    Cannot predict now.
-    Concentrate and ask again.
-
-  ## Very negative
-    Don't count on it.
-    My reply is no.
-    My sources say no.
-    Outlook not so good.
-    Very doubtful.
-*/
+// /**
+
+//   Let's peer into the future using a Magic 8 Ball!
+//   https://en.wikipedia.org/wiki/Magic_8-Ball 
+
+//   There are a few steps to being able view the future though:
+//   * Ask a question
+//   * Shake the ball
+//   * Get an answer
+//   * Decide if it's positive or negative
+
+//   The question can be anything, but the answers are fixed,
+//   and have different levels of positivity or negativity.
+
+//   Below are the possible answers:
+
+
+  let veryPositive = [
+
+    "It is certain.",
+    "It is decidedly so.",
+    "Without a doubt.",
+    "Yes - definitely.",
+    "You may rely on it."
+  ]
+
+  let positive = [
+
+    "Positive",
+    "As I see it, yes.",
+    "Most likely.",
+    "Outlook good.",
+    "Yes.",
+    "Signs point to yes."
+  ]
+
+  let negative = [
+
+    "Reply hazy, try again.",
+    "Ask again later.",
+    "Better not tell you now.",
+    "Cannot predict now.",
+    "Concentrate and ask again."
+  ]
+
+  let veryNegative = [
+
+    "Don't count on it.",
+    "My reply is no.",
+    "My sources say no.",
+    "Outlook not so good.",
+    "Very doubtful."
+  ]
+
 
 // This should log "The ball has shaken!"
 // and return the answer.
+
 function shakeBall() {
-  //Write your code in here
-}
+  console.log("The ball has shaken!");
+  // const allAnswers = veryPositive.concat(positive, negative, veryNegative);
+  const allAnswers = [...veryPositive, ...positive, ...negative, ...veryNegative];
+  let answer = allAnswers [Math.floor(Math.random()*allAnswers.length)];
+  // console.log(prediction);
+  return answer;
+  
+  }
 
 /* 
   This function should say whether the answer it is given is
@@ -59,9 +76,24 @@ function shakeBall() {
   This function should expect to be called with any value which was returned by the shakeBall function.
 */
 function checkAnswer(answer) {
+  if (veryPositive.indexOf(answer) >= 0 ) {
+    return "very positive";
   //Write your code in here
+  } else if (positive.indexOf(answer) >= 0) {
+     return "positive";
+     } else if (negative.indexOf(answer) >= 0) {
+      return "negative";
+     } else {
+      return "very negative";
+     }
+
+     
 }
 
+
+console.log(checkAnswer(shakeBall()));
+
+
 /* 
 ==================================
 ======= TESTS - DO NOT MODIFY =====
diff --git a/mandatory/1-syntax-errors.js b/mandatory/1-syntax-errors.js
index d9e004465..6fc5c93ba 100644
--- a/mandatory/1-syntax-errors.js
+++ b/mandatory/1-syntax-errors.js
@@ -1,16 +1,17 @@
 // There are syntax errors in this code - can you fix it to pass the tests?
 
-function addNumbers(a b c) {
+function addNumbers(a, b, c) {
   return a + b + c;
 }
 
-function introduceMe(name, age)
-  return `Hello, my {name}` is "and I am $age years old`;
+function introduceMe(name, age) {
+  return `Hello, my name is ${name} and I am ${age} years old`;
+}
+  
 
 function getTotal(a, b) {
-  total = a ++ b;
-
-  return "The total is total";
+  total = a + b;
+  return `The total is ${total}`;
 }
 
 /* 
diff --git a/mandatory/2-logic-error.js b/mandatory/2-logic-error.js
index 9eb8c8cd7..5152c982c 100644
--- a/mandatory/2-logic-error.js
+++ b/mandatory/2-logic-error.js
@@ -1,16 +1,16 @@
 // The syntax for these functions is valid but there are some errors, find them and fix them
 
 function trimWord(word) {
-  return wordtrim();
+  return word.trim();
 }
 
 function getStringLength(word) {
-  return "word".length();
+  return word.length;
 }
 
 function multiply(a, b, c) {
-  a * b * c;
-  return;
+  
+  return a * b * c;
 }
 
 /* 
diff --git a/mandatory/3-function-output.js b/mandatory/3-function-output.js
index 5a953ba60..535d1f8b3 100644
--- a/mandatory/3-function-output.js
+++ b/mandatory/3-function-output.js
@@ -2,13 +2,17 @@
 function getRandomNumber() {
   return Math.random() * 10;
 }
+// returns a random number between 0 (inclusive),  and 1 (exclusive)
 
 // Add comments to explain what this function does. You're meant to use Google!
 function combine2Words(word1, word2) {
   return word1.concat(word2);
 }
+// The concat() method is used to merge two or more arrays. This method does not change the existing arrays, but instead returns a new array.
 
 function concatenate(firstWord, secondWord, thirdWord) {
+  return firstWord.concat(" ", secondWord, " ", thirdWord);
+
   // Write the body of this function to concatenate three words together.
   // Look at the test case below to understand what this function is expected to return.
 }
diff --git a/mandatory/4-tax.js b/mandatory/4-tax.js
index ba77c7ae2..6eadbdccb 100644
--- a/mandatory/4-tax.js
+++ b/mandatory/4-tax.js
@@ -5,7 +5,9 @@
   Sales tax is 20% of the price of the product.
 */
 
-function calculateSalesTax() {}
+function calculateSalesTax(netPrice) {
+  return netPrice * 1.2;
+}
 
 /*
   CURRENCY FORMATTING
@@ -17,7 +19,9 @@ function calculateSalesTax() {}
   Remember that the prices must include the sales tax (hint: you already wrote a function for this!)
 */
 
-function addTaxAndFormatCurrency() {}
+function addTaxAndFormatCurrency(netPrice) {
+  return `£${calculateSalesTax(netPrice).toFixed(2)}`;
+}
 
 /* 
 ===================================================