diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..b99ea43cf 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,4 +1,7 @@
 // Predict and explain first...
+//Prediction: The will be an error at ${address[0]}.
+//Explanation: calling an object using the index as in array. Instead we should use the dot method(.address) or the brackets["address"].
+
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +15,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..3a540064c 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// Prediction: Going to shows an error in the for loop.
+// Explanation: we should have used the for .. in method (The for...in statement iterates over all enumerable string properties of an object (ignoring properties keyed by symbols), including inherited enumerable properties.)
 
 // This program attempts to log out all the property values in the object.
 // But it isn't working. Explain why first and then fix the problem
@@ -11,6 +13,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
-  console.log(value);
+for (const value in author){
+  console.log(`${value}: ${author[value]}`);
 }
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..bcc190551 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// Prediction: An error in logging out the ingredients.
+// Explanation: Because of the way to get the value or an element from an array should used the dot notation for example and reach each element using its index.
 
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
@@ -12,4 +14,6 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);
+
+module.exports = recipe;
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..33e75c7b5 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,10 @@
-function contains() {}
+function contains(input, propertyName) {
+
+    if (input !== null && typeof input === "object" && !Array.isArray(input)) {
+    return Object.prototype.hasOwnProperty.call(input, propertyName);
+  }
+
+  return false;
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..1f8310810 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -17,19 +17,49 @@ as the object doesn't contains a key of 'c'
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
 
+test("given an object contains a property name, returns true", () => {
+    const input = { a: 1, b: 2 };
+    const propertyName = "a";
+    expect(contains(input, propertyName)).toBe(true);
+});
+
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+
+test("given an empty object, returns false", () => {
+    const input = {};
+    const propertyName = "a";
+    expect(contains(input, propertyName)).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
 
+test("given an object contains a property name, returns true", () => {
+    const input = { a: 1, b: 2 };
+    const propertyName = "a";
+    expect(contains(input, propertyName)).toBe(true);
+});
+
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
 
+test("given an object does not contain a property name, returns false", () => {
+    const input = { a: 1, b: 2 };
+    const propertyName = "c";
+    expect(contains(input, propertyName)).toBe(false);
+});
+
+
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+
+test("given invalid parameters like an array, returns false", () => {
+    const input = [1, 2, 3];     
+    const propertyName = "0";    
+    expect(contains(input, propertyName)).toBe(false);
+});
\ No newline at end of file
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..1accb2d54 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,11 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  const lookup = {};
+
+  for (const [country, currency] of pairs) {
+    lookup[country] = currency;
+  }
+
+  return lookup;
 }
 
-module.exports = createLookup;
+module.exports = createLookup;
\ No newline at end of file
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..0838285d4 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,7 +1,20 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
+test("creates a country currency code lookup for multiple codes", () => {
+  const input = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+
+  const result = createLookup(input);
+
+  expect(result).toEqual({
+    US: "USD",
+    CA: "CAD",
+    GB: "GBP",
+  });
+});
 /*
 
 Create a lookup object of key value pairs from an array of code pairs
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..5a2783014 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,12 +1,33 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
+
+  if (!queryString) return queryParams;
+
+  if (queryString.startsWith("?")) {
+    queryString = queryString.slice(1);
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    if (!pair) continue;
+
+    const firstEq = pair.indexOf("=");
+
+    let key;
+    let value;
+
+    if (firstEq === -1) {
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, firstEq);
+      value = pair.slice(firstEq + 1);
+    }
+
+    key = decodeURIComponent(key);
+    value = decodeURIComponent(value);
+
     queryParams[key] = value;
   }
 
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..42ec0039d 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -10,3 +10,31 @@ test("parses querystring values containing =", () => {
     "equation": "x=y+1",
   });
 });
+
+test("parses multiple key=value pairs", () => {
+  expect(parseQueryString("a=1&b=2")).toEqual({ a: "1", b: "2" });
+});
+
+test("handles empty value (a=)", () => {
+  expect(parseQueryString("a=")).toEqual({ a: "" });
+});
+
+test("handles key with no '=' (a)", () => {
+  expect(parseQueryString("a")).toEqual({ a: "" });
+});
+
+test("last value wins for repeated keys", () => {
+  expect(parseQueryString("a=1&a=2")).toEqual({ a: "2" });
+});
+
+test("supports leading question mark", () => {
+  expect(parseQueryString("?a=1&b=2")).toEqual({ a: "1", b: "2" });
+});
+
+test("ignores empty pairs from trailing or consecutive &", () => {
+  expect(parseQueryString("a=1&&b=2&")).toEqual({ a: "1", b: "2" });
+});
+
+test("handles empty key (=value) producing empty-string key", () => {
+  expect(parseQueryString("=value")).toEqual({ "": "value" });
+});
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..dc79bc3dd 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,19 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("tally expects an array");
+  }
+
+  const counts = Object.create(null);
+
+  for (const item of items) {
+    if (counts[item] === undefined) {
+      counts[item] = 1;
+    } else {
+      counts[item] += 1;
+    }
+  }
+
+  return counts;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..8a8893067 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -19,16 +19,37 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
+test("tally returns counts for each unique item", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({
+    a: 2,
+    b: 1,
+    c: 1,
+  });
+});
 
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+test("tally on an empty array returns an empty object", () => {
+  expect(tally([])).toEqual({});
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally counts each unique item", () => {
+  expect(tally(["a", "a", "b", "c", "a"])).toEqual({
+    a: 3,
+    b: 1,
+    c: 1,
+  });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws an error when given a non-array", () => {
+  expect(() => tally("not an array")).toThrow();
+  expect(() => tally(123)).toThrow();
+  expect(() => tally({})).toThrow();
+});
\ No newline at end of file
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..7c7aa6230 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -16,14 +16,52 @@ function invert(obj) {
   return invertedObj;
 }
 
-// a) What is the current return value when invert is called with { a : 1 }
+// a) What is the current return value when invert is called with { a : 1 } >> { key: 1 }
 
-// b) What is the current return value when invert is called with { a: 1, b: 2 }
+// b) What is the current return value when invert is called with { a: 1, b: 2 } >> { key: 2 }
 
-// c) What is the target return value when invert is called with {a : 1, b: 2}
+// c) What is the target return value when invert is called with {a : 1, b: 2} >> { "1": "a", "2": "b" }
 
-// c) What does Object.entries return? Why is it needed in this program?
+// c) What does Object.entries return? Why is it needed in this program? >> Object.entries returns an array of key-value paris.
 
-// d) Explain why the current return value is different from the target output
+// d) Explain why the current return value is different from the target output >> Because invertedObj.key = value creates a property called (key) instead of using hte variable key.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// The fixed code:
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+module.exports = invert;
+
+// Tests:
+const invert = require("./invert.js");
+
+// Single key
+test("invert works for one key-value pair", () => {
+  expect(invert({ a: 1 })).toEqual({ "1": "a" });
+});
+
+// Multiple keys
+test("invert swaps keys and values for multiple pairs", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({
+    "1": "a",
+    "2": "b",
+  });
+});
+
+// Empty object
+test("invert of an empty object returns empty", () => {
+  expect(invert({})).toEqual({});
+});
+
+// Values become string keys
+test("invert always returns string keys", () => {
+  expect(invert({ x: 10 })).toEqual({ "10": "x" });
+});
diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..f805275ba 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -26,3 +26,51 @@
 
 3. Order the results to find out which word is the most common in the input
 */
+
+
+
+/* The implementation:
+function countWords(str) {
+  const result = {};
+
+  if (!str || str.trim().length === 0) {
+    return result;
+  }
+
+  const words = str.split(" ");
+
+  for (const word of words) {
+    if (result[word] === undefined) {
+      result[word] = 1;
+    } else {
+      result[word] += 1;
+    }
+  }
+
+  return result;
+}
+
+module.exports = countWords;
+*/
+
+/* The tests:
+
+const countWords = require("./countWords.js");
+
+test("counts words from a string", () => {
+  expect(countWords("you and me and you")).toEqual({
+    you: 2,
+    and: 2,
+    me: 1,
+  });
+});
+
+test("returns empty object for empty string", () => {
+  expect(countWords("")).toEqual({});
+  expect(countWords("   ")).toEqual({});
+});
+
+test("counts correctly with single word", () => {
+  expect(countWords("hello")).toEqual({ hello: 1 });
+});
+*/
\ No newline at end of file
diff --git a/Sprint-2/stretch/mode.js b/Sprint-2/stretch/mode.js
index 3f7609d79..f1dfd8bec 100644
--- a/Sprint-2/stretch/mode.js
+++ b/Sprint-2/stretch/mode.js
@@ -8,29 +8,38 @@
 // refactor calculateMode by splitting up the code
 // into smaller functions using the stages above
 
-function calculateMode(list) {
-  // track frequency of each value
-  let freqs = new Map();
-
-  for (let num of list) {
-    if (typeof num !== "number") {
-      continue;
-    }
+// Stage 1: count frequencies
+function countFrequencies(list) {
+  const freqs = new Map();
 
+  for (const num of list) {
+    if (typeof num !== "number") continue;
     freqs.set(num, (freqs.get(num) || 0) + 1);
   }
 
-  // Find the value with the highest frequency
+  return freqs;
+}
+
+// Stage 2: find the value with highest frequency
+function findMode(freqs) {
   let maxFreq = 0;
   let mode;
-  for (let [num, freq] of freqs) {
+
+  for (const [num, freq] of freqs.entries()) {
     if (freq > maxFreq) {
-      mode = num;
       maxFreq = freq;
+      mode = num;
     }
   }
 
   return maxFreq === 0 ? NaN : mode;
 }
 
+// Main function
+function calculateMode(list) {
+  const freqs = countFrequencies(list);
+  return findMode(freqs);
+}
+
 module.exports = calculateMode;
+
diff --git a/Sprint-2/stretch/till.js b/Sprint-2/stretch/till.js
index 6a08532e7..d47c4b906 100644
--- a/Sprint-2/stretch/till.js
+++ b/Sprint-2/stretch/till.js
@@ -22,10 +22,32 @@ const till = {
 };
 const totalAmount = totalTill(till);
 
-// a) What is the target output when totalTill is called with the till object
+// a) What is the target output when totalTill is called with the till object >> "£4.40"
 
-// b) Why do we need to use Object.entries inside the for...of loop in this function?
+// b) Why do we need to use Object.entries inside the for...of loop in this function? >> To iterate over both the keys (coin types) and values (quantities) of the till object.
 
-// c) What does coin * quantity evaluate to inside the for...of loop?
+// c) What does coin * quantity evaluate to inside the for...of loop? >> It evaluates to NaN because coin is a string (e.g., "1p") and cannot be directly multiplied by a number (quantity).
 
 // d) Write a test for this function to check it works and then fix the implementation of totalTill
+
+// Fixed implementation
+function totalTillFixed(till) {
+  let total = 0;
+
+  for (const [coin, quantity] of Object.entries(till)) {
+    const coinValue = parseInt(coin);
+    total += coinValue * quantity;
+  }
+
+  return `£${(total / 100).toFixed(2)}`;
+}
+
+// Test
+const tillTest = {
+  "1p": 10,
+  "5p": 6,
+  "50p": 4,
+  "20p": 10,
+};
+const totalAmountTest = totalTillFixed(tillTest);
+console.log(totalAmountTest);