diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index b22590bc6..db759d5ba 100644
--- a/Sprint-1/fix/median.js
+++ b/Sprint-1/fix/median.js
@@ -6,9 +6,31 @@
 // or 'list' has mixed values (the function is expected to sort only numbers).
 
 function calculateMedian(list) {
-  const middleIndex = Math.floor(list.length / 2);
-  const median = list.splice(middleIndex, 1)[0];
-  return median;
+  // Validate input: must be an array
+  if (!Array.isArray(list)) {
+    return null;
+  }
+
+  // Filter out non-numeric values
+  const numbers = list.filter((item) => typeof item === "number");
+
+  // If no numeric values, return null
+  if (numbers.length === 0) {
+    return null;
+  }
+
+  // Sort numbers without mutating original list
+  const sorted = [...numbers].sort((a, b) => a - b);
+
+  const middleIndex = Math.floor(sorted.length / 2);
+
+  // Odd length → return middle number
+  if (sorted.length % 2 !== 0) {
+    return sorted[middleIndex];
+  }
+
+  // Even length → average of two middle numbers
+  return (sorted[middleIndex - 1] + sorted[middleIndex]) / 2;
 }
 
 module.exports = calculateMedian;
diff --git a/Sprint-1/implement/dedupe.js b/Sprint-1/implement/dedupe.js
index 781e8718a..209465014 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1 +1,5 @@
-function dedupe() {}
+function dedupe(arr) {
+  return [...new Set(arr)];
+}
+
+module.exports = dedupe;
\ No newline at end of file
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index 6dd76378e..ceacf7c5a 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,4 +1,9 @@
 function findMax(elements) {
+  const numbers = elements.filter((item) => typeof item === "number");
+  if (numbers.length === 0) {
+    return -Infinity;
+  }
+  return Math.max(...numbers);
 }
 
 module.exports = findMax;
diff --git a/Sprint-1/implement/max.test.js b/Sprint-1/implement/max.test.js
index 82f18fd88..ebfabf0fa 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -16,28 +16,49 @@ const findMax = require("./max.js");
 // When passed to the max function
 // Then it should return -Infinity
 // Delete this test.todo and replace it with a test.
-test.todo("given an empty array, returns -Infinity");
+//test.todo("given an empty array, returns -Infinity");
+test("given an empty array, returns -Infinity", () => {
+  expect(findMax([])).toBe(-Infinity);
+});
 
 // Given an array with one number
 // When passed to the max function
 // Then it should return that number
+test("given an array with one number, returns that number", () => {
+  expect(findMax([42])).toBe(42);
+});
 
 // Given an array with both positive and negative numbers
 // When passed to the max function
 // Then it should return the largest number overall
+test("given an array with positive and negative numbers, returns the largest", () => {
+  expect(findMax([-10, 5, 3, -2])).toBe(5);
+});
 
 // Given an array with just negative numbers
 // When passed to the max function
 // Then it should return the closest one to zero
+test("given an array with only negative numbers, returns the closest to zero", () => {
+  expect(findMax([-10, -3, -20])).toBe(-3);
+});
 
 // Given an array with decimal numbers
 // When passed to the max function
 // Then it should return the largest decimal number
+test("given an array with decimal numbers, returns the largest decimal", () => {
+  expect(findMax([1.2, 3.5, 2.8])).toBe(3.5);
+});
 
 // Given an array with non-number values
 // When passed to the max function
 // Then it should return the max and ignore non-numeric values
+test("given an array with non-number values, ignores them and returns the max", () => {
+  expect(findMax(['hey', 10, 'hi', 60, 10])).toBe(60);
+});
 
 // Given an array with only non-number values
 // When passed to the max function
 // Then it should return the least surprising value given how it behaves for all other inputs
+test("given an array with only non-number values, returns -Infinity", () => {
+  expect(findMax(['a', 'b', null, undefined])).toBe(-Infinity);
+});
\ No newline at end of file
diff --git a/Sprint-1/implement/sum.js b/Sprint-1/implement/sum.js
index 9062aafe3..7d4ec4186 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,4 +1,9 @@
 function sum(elements) {
+  const numbers = elements.filter((item) => typeof item === "number");
+  if (numbers.length === 0) {
+    return 0;
+  }
+  return numbers.reduce((total, num) => total + num, 0);
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index dd0a090ca..32bab4ade 100644
--- a/Sprint-1/implement/sum.test.js
+++ b/Sprint-1/implement/sum.test.js
@@ -13,24 +13,42 @@ const sum = require("./sum.js");
 // Given an empty array
 // When passed to the sum function
 // Then it should return 0
-test.todo("given an empty array, returns 0")
+// test.todo("given an empty array, returns 0")
+test("given an empty array, returns 0", () => {
+  expect(sum([])).toBe(0);
+});
 
 // Given an array with just one number
 // When passed to the sum function
 // Then it should return that number
+test("given an array with one number, returns that number", () => {
+  expect(sum([42])).toBe(42);
+});
 
 // Given an array containing negative numbers
 // When passed to the sum function
 // Then it should still return the correct total sum
+test("given an array with negative numbers, returns the correct total", () => {
+  expect(sum([-5, 10, -3])).toBe(2);
+});
 
 // Given an array with decimal/float numbers
 // When passed to the sum function
 // Then it should return the correct total sum
+test("given an array with decimal numbers, returns the correct total", () => {
+  expect(sum([1.5, 2.5, 3.1])).toBe(7.1);
+});
 
 // Given an array containing non-number values
 // When passed to the sum function
 // Then it should ignore the non-numerical values and return the sum of the numerical elements
+test("given an array with non-number values, ignores them and returns the sum of numbers", () => {
+  expect(sum(["hey", 10, "hi", 60, 10])).toBe(80);
+});
 
 // Given an array with only non-number values
 // When passed to the sum function
 // Then it should return the least surprising value given how it behaves for all other inputs
+test("given an array with only non-number values, returns 0", () => {
+  expect(sum(["a", null, undefined, "b"])).toBe(0);
+});
diff --git a/Sprint-1/refactor/includes.js b/Sprint-1/refactor/includes.js
index 29dad81f0..8c9ae2e66 100644
--- a/Sprint-1/refactor/includes.js
+++ b/Sprint-1/refactor/includes.js
@@ -1,8 +1,7 @@
 // Refactor the implementation of includes to use a for...of loop
 
 function includes(list, target) {
-  for (let index = 0; index < list.length; index++) {
-    const element = list[index];
+  for (const element of list) {
     if (element === target) {
       return true;
     }
diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..a3f63cd92 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -4,6 +4,19 @@
 // but it isn't working...
 // Fix anything that isn't working
 
+/*const address = {
+  houseNumber: 42,
+  street: "Imaginary Road",
+  city: "Manchester",
+  country: "England",
+  postcode: "XYZ 123",
+};
+
+console.log(`My house number is ${address[0]}`); */
+
+// The line "address[0]" is wrong. Because address is an object not an array, so "address[0]" is undefined. The output will be "My house number is undefined".
+
+// Corrected code
 const address = {
   houseNumber: 42,
   street: "Imaginary Road",
@@ -12,4 +25,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
\ No newline at end of file
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..37a05131d 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -3,7 +3,7 @@
 // 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
 
-const author = {
+/* const author = {
   firstName: "Zadie",
   lastName: "Smith",
   occupation: "writer",
@@ -14,3 +14,21 @@ const author = {
 for (const value of author) {
   console.log(value);
 }
+*/
+
+// Prediction and Explanation
+/* The line "for (const value of author) {console.log(value);}" will not work because for-of is used only for iterable things, e.g: arrays, strings, maps, sets.
+But author is a plain object (created with {}), and plain objects are not iterable. So Javascript throws: TypeError: author is not iterable because objects don't have a natural order to loop through. */
+
+// Corrected code
+const author = {
+  firstName: "Zadie",
+  lastName: "Smith",
+  occupation: "writer",
+  age: 40,
+  alive: true,
+};
+
+for (const value of Object.values(author)) {
+  console.log(value);
+} 
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..ab5c9d0cd 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -4,7 +4,7 @@
 // Each ingredient should be logged on a new line
 // How can you fix it?
 
-const recipe = {
+/*const recipe = {
   title: "bruschetta",
   serves: 2,
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
@@ -13,3 +13,26 @@ const recipe = {
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
 ${recipe}`);
+*/
+
+// Prediction and Explanation
+/* 
+The line inside the template string: ${recipe} does not print the ingredients. 
+Instead, JavaScript converts the entire recipe object into a string, which becomes "[object Object]". This happens 
+because plain objects {} are not automatically converted into readable text. The program should print each ingredient on a new line, but the current code 
+never loops through recipe.ingredients, so nothing is printed correctly.
+*/
+
+// Corrected code
+const recipe = {
+  title: "bruschetta",
+  serves: 2,
+  ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
+};
+
+console.log(`${recipe.title} serves ${recipe.serves}
+ingredients:`);
+
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..05f18e140 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,10 @@
-function contains() {}
+function contains(obj, prop) {
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return false;
+  }
+
+  return obj.hasOwnProperty(prop);
+}
 
 module.exports = contains;
+
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..9a232aa56 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -16,20 +16,47 @@ as the object doesn't contains a key of 'c'
 // Given a contains function
 // When passed an object and a property name
 // Then it should return true if the object contains the property, false otherwise
+test("returns true when object contains the property", () => {
+  const obj = { a: 1, b: 2 };
+  expect(contains(obj, "a")).toBe(true);
+});
+
+test("returns false when object does not contain the property", () => {
+  const obj = { a: 1, b: 2 };
+  expect(contains(obj, "c")).toBe(false);
+});
+
 
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+// test.todo("contains on empty object returns false");
+test("contains on empty object returns false", () => {
+  expect(contains({}, "a")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("returns true when object contains the property", () => {
+  const obj = { a: 1, b: 2 };
+  expect(contains(obj, "a")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("returns false when object does not contain the property", () => {
+  const obj = { a: 1, b: 2 };
+  expect(contains(obj, "c")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("returns false for invalid parameters like an array", () => {
+  expect(contains([], "a")).toBe(false);
+  expect(contains(null, "a")).toBe(false);
+  expect(contains(123, "a")).toBe(false);
+  expect(contains("hello", "a")).toBe(false);
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..48466c281 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -5,7 +5,7 @@
 // Then it should swap the keys and values in the object
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
-
+/*
 function invert(obj) {
   const invertedObj = {};
 
@@ -15,15 +15,31 @@ 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 } - The current return value is { 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 } - The current return value is { 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} - The target return value is { "1": "a", "2": "b" }
 
 // c) What does Object.entries return? Why is it needed in this program?
+/* Object.entries(obj) returns an array of [key, value] pairs. Example: Object.entries({ a:1, b:2 }) returns [["a", 1], ["b", 2]].
+It is needed because the loop "for (const [key, value] of Object.entries(obj))" let's each pair destructure easily.
+*/
 
-// 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 - It is because this line "invertedObj.key = value;" uses literal string "key instead of the variable key" which is a wrong property name,
+// instead of this "invertedObj[value] = key;"
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+module.exports = invert;
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..f8643a570
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,17 @@
+const invert = require("./invert.js");
+
+test("inverts a single key-value pair", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+
+test("inverts multiple key-value pairs", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+});
+
+test("handles empty objects", () => {
+  expect(invert({})).toEqual({});
+});
+
+test("handles string values", () => {
+  expect(invert({ x: "hello" })).toEqual({ hello: "x" });
+});