diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index b22590bc6..26435293f 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;
+
+  // First: ensure input is actually an array BEFORE calling array methods
+  if (!Array.isArray(list)) {
+    return null;
+  }
+
+  // Filter only number values
+  const numbers = list.filter((item) => typeof item === "number");
+
+  // Return null if no valid numbers exist
+  if (numbers.length === 0) {
+    return null;
+  }
+
+  // Sort values without modifying original input
+  const sortedNumbers = [...numbers].sort((a, b) => a - b);
+  const middleIndex = Math.floor(sortedNumbers.length / 2);
+
+  // Odd length → return middle value
+  if (sortedNumbers.length % 2 !== 0) {
+    return sortedNumbers[middleIndex];
+  }
+
+  // Even length → return average of two middle values
+  return (sortedNumbers[middleIndex - 1] + sortedNumbers[middleIndex]) / 2;
 }
 
 module.exports = calculateMedian;
diff --git a/Sprint-1/implement/dedupe.js b/Sprint-1/implement/dedupe.js
index 781e8718a..5f74993a0 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1 +1,20 @@
-function dedupe() {}
+function dedupe(arr) {
+    
+  if (!Array.isArray(arr)) return null;
+
+  // Create a new result array
+  const result = [];
+
+  // Loop through original array
+  for (const item of arr) {
+    // Add only the first occurrence of each element
+    if (!result.includes(item)) {
+      result.push(item);
+    }
+  }
+
+  // Return the deduplicated array
+  return result;
+}
+
+module.exports = dedupe;
diff --git a/Sprint-1/implement/dedupe.test.js b/Sprint-1/implement/dedupe.test.js
index 23e0f8638..2daa8447b 100644
--- a/Sprint-1/implement/dedupe.test.js
+++ b/Sprint-1/implement/dedupe.test.js
@@ -16,12 +16,26 @@ E.g. dedupe([1, 2, 1]) target output: [1, 2]
 // Given an empty array
 // When passed to the dedupe function
 // Then it should return an empty array
-test.todo("given an empty array, it returns an empty array");
+test("given an empty array, it returns an empty array", () => {
+  expect(dedupe([])).toEqual([]);
+});
 
 // Given an array with no duplicates
 // When passed to the dedupe function
 // Then it should return a copy of the original array
+test("given an array with no duplicates, returns a copy", () => {
+  const arr = [1, 2, 3];
+  const result = dedupe(arr);
+
+  expect(result).toEqual([1, 2, 3]);
+  expect(result).not.toBe(arr); // ensure it's a new array, not the same reference
+});
 
 // Given an array with strings or numbers
 // When passed to the dedupe function
 // Then it should remove the duplicate values, preserving the first occurence of each element
+test("removes duplicate values and preserves first occurrence", () => {
+  expect(dedupe(["a", "a", "a", "b", "b", "c"])).toEqual(["a", "b", "c"]);
+  expect(dedupe([5, 1, 1, 2, 3, 2, 5, 8])).toEqual([5, 1, 2, 3, 8]);
+  expect(dedupe([1, 2, 1])).toEqual([1, 2]);
+});
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index 6dd76378e..2d82ee2f4 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,4 +1,15 @@
 function findMax(elements) {
+  // If elements is not an array, return -Infinity (least surprising behaviour)
+  if (!Array.isArray(elements)) return -Infinity;
+
+  // Filter numeric values only
+  const numbers = elements.filter((item) => typeof item === "number");
+
+  // If no numeric values found, return -Infinity
+  if (numbers.length === 0) return -Infinity;
+
+  // Return the maximum number
+  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..3f2585667 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -16,28 +16,48 @@ 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("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 mixed positive and negative numbers, returns the largest", () => {
+  expect(findMax([-10, 5, 20, -3])).toBe(20);
+});
 
 // Given an array with just negative numbers
 // When passed to the max function
 // Then it should return the closest one to zero
+test("given only negative numbers, returns the one closest to zero", () => {
+  expect(findMax([-50, -10, -3, -100])).toBe(-3);
+});
 
 // Given an array with decimal numbers
 // When passed to the max function
 // Then it should return the largest decimal number
+test("given decimal numbers, returns the largest value", () => {
+  expect(findMax([1.5, 2.7, 2.6, 0.1])).toBe(2.7);
+});
 
 // 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("ignores non-numeric values and returns the maximum number", () => {
+  expect(findMax(["hi", 10, "wow", 30, 5])).toBe(30);
+});
 
 // 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 only non-number values, returns -Infinity", () => {
+  expect(findMax(["a", "b", {}, null])).toBe(-Infinity);
+});
diff --git a/Sprint-1/implement/sum.js b/Sprint-1/implement/sum.js
index 9062aafe3..4a8c2692d 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,4 +1,11 @@
 function sum(elements) {
+  // If input is not an array, return 0 (least surprising behaviour)
+  if (!Array.isArray(elements)) return 0;
+
+  // Sum only numeric values
+  return elements.reduce((total, item) => {
+    return typeof item === "number" ? total + item : total;
+  }, 0);
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index dd0a090ca..0ab3313e5 100644
--- a/Sprint-1/implement/sum.test.js
+++ b/Sprint-1/implement/sum.test.js
@@ -13,24 +13,41 @@ 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("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 one number, returns that number", () => {
+  expect(sum([7])).toBe(7);
+});
 
 // Given an array containing negative numbers
 // When passed to the sum function
 // Then it should still return the correct total sum
+test("sums negative numbers correctly", () => {
+  expect(sum([-5, -10, 3])).toBe(-12);
+});
 
 // Given an array with decimal/float numbers
 // When passed to the sum function
 // Then it should return the correct total sum
+test("sums decimal numbers correctly", () => {
+  expect(sum([1.5, 2.25, 3.25])).toBe(7);
+});
 
 // 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("ignores non-number values and sums only numbers", () => {
+  expect(sum(["hi", 10, "wow", 20, null, 5])).toBe(35);
+});
 
 // 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 only non-number values, returns 0", () => {
+  expect(sum(["a", {}, null, undefined])).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..7a4b4a680 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,4 +1,8 @@
 // Predict and explain first...
+// Prediction: The code will print "My house number is undefined".
+// Explanation: The code uses address[0], but address is an object, not an array.
+// Objects cannot be accessed using numeric indexes. Therefore address[0] does not exist
+// and evaluates to undefined.
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +16,5 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
+// Expected output: My house number is 42
\ No newline at end of file