diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index b22590bc6..eb62ed801 100644
--- a/Sprint-1/fix/median.js
+++ b/Sprint-1/fix/median.js
@@ -6,9 +6,22 @@
 // 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;
+  // Return null for non arrays
+  if (!Array.isArray(list)) return null;
+  // Filter to only numeric values
+  const nums = list.filter((x) => typeof x === "number" && isFinite(x));
+  // Return null if no valid numbers remain
+  if (nums.length === 0) return null;
+  // Sort the numbers in ascending order
+  // filter already returns a new array so need to spread before spreading
+  const sorted = nums.sort((a, b) => a - b);
+  // Find the middle index of the sorted array
+  const middleIndex = Math.floor(sorted.length / 2);
+  // If odd length, return the middle index
+  // If even length, return the average of the two middle elements
+  return sorted.length % 2 !== 0
+    ? sorted[middleIndex]
+    : (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..f152f8185 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1 +1,9 @@
-function dedupe() {}
+function dedupe(arr) {
+  // Return null if the input is not an array
+  if (!Array.isArray(arr)) return null;
+  // Use Set to remove duplicates,
+  // then spread back into a new array
+  return [...new Set(arr)];
+}
+
+module.exports = dedupe;
diff --git a/Sprint-1/implement/dedupe.test.js b/Sprint-1/implement/dedupe.test.js
index 23e0f8638..6f5ef6565 100644
--- a/Sprint-1/implement/dedupe.test.js
+++ b/Sprint-1/implement/dedupe.test.js
@@ -16,12 +16,27 @@ 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, it returns a copy of the original array", () => {
+  const input = [1, 2, 3];
+  const result = dedupe(input);
+  // Check the contents match a hardcoded expected value, not the input itself
+  expect(result).toEqual([1, 2, 3]);
+  // Check it's a different array, not the same reference
+  expect(result).not.toBe(input);
+});
 
 // 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("given an array with duplicate numbers or strings, it removes duplicates preserving first occurence", () => {
+  expect(dedupe([5, 1, 1, 2, 3, 2, 5, 8])).toEqual([5, 1, 2, 3, 8]);
+  expect(dedupe(["a", "a", "a", "b", "b", "c"])).toEqual(["a", "b", "c"]);
+  expect(dedupe([1, 2, 1])).toEqual([1, 2]);
+});
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index 6dd76378e..6e1ccee50 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,4 +1,8 @@
 function findMax(elements) {
+  // Filter to only numeric values
+  const nums = elements.filter((x) => typeof x === "number" && isFinite(x));
+  // Math.max with no arguments returns -Infinity, which handles empty arrays as well
+  return Math.max(...nums);
 }
 
 module.exports = findMax;
diff --git a/Sprint-1/implement/max.test.js b/Sprint-1/implement/max.test.js
index 82f18fd88..f5b52ee9c 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -16,28 +16,51 @@ 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([])).toEqual(-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])).toEqual(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([30, 50, 10, 40])).toEqual(50);
+  expect(findMax([-10, 5, 3, -2])).toEqual(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, -7])).toEqual(-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, return the largest decimal number", () => {
+  expect(findMax([1.5, 2.7, 0.3])).toEqual(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("given an array with non-numeric values, returns the max and ignores non-numerics", () => {
+  expect(findMax(["hey", 10, "hi", 60, 10])).toEqual(60);
+  // "300" looks numeric but is a string, so it should be ignored
+  expect(findMax([10, "300", 20])).toEqual(20);
+});
 
 // 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-numeric values, returns -Infinity", () => {
+  expect(findMax(["hey", "hi", null, undefined])).toEqual(-Infinity);
+});
diff --git a/Sprint-1/implement/sum.js b/Sprint-1/implement/sum.js
index 9062aafe3..3fa5cedf9 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,4 +1,9 @@
 function sum(elements) {
+  // Filter to only numeric values,
+  // then reduce to a total
+  return elements
+    .filter((x) => typeof x === "number" && isFinite(x))
+    .reduce((total, x) => total + x, 0);
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index dd0a090ca..436f4b3c4 100644
--- a/Sprint-1/implement/sum.test.js
+++ b/Sprint-1/implement/sum.test.js
@@ -13,24 +13,44 @@ 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([])).toEqual(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])).toEqual(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 sum", () => {
+  expect(sum([-10, -20, -30])).toEqual(-60);
+  expect(sum([-5, -3, -2])).toEqual(-10);
+});
 
 // 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 sum", () => {
+  expect(sum([1.5, 2.5, 3.0])).toEqual(7);
+  // toBeCloseTo is used for floating point calculations to avoid precision issues
+  expect(sum([1.2, 0.6, 0.005])).toBeCloseTo(1.805);
+});
 
 // 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-numeric values, ignores them and returns the sum", () => {
+  expect(sum(["hey", 10, "hi", 60, 10])).toEqual(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-numeric values, returns 0", () => {
+  expect(sum(["hey", "hi", null, undefined])).toEqual(0);
+});
diff --git a/Sprint-1/refactor/includes.js b/Sprint-1/refactor/includes.js
index 29dad81f0..2e60f61a6 100644
--- a/Sprint-1/refactor/includes.js
+++ b/Sprint-1/refactor/includes.js
@@ -1,12 +1,14 @@
 // 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];
+  // Iterate directly over each element in the list
+  for (const element of list) {
+    // Return true as soon as we find a match
     if (element === target) {
       return true;
     }
   }
+  // Target was not found in the list
   return false;
 }
 
diff --git a/Sprint-1/refactor/includes.test.js b/Sprint-1/refactor/includes.test.js
index 812158470..3d6babe53 100644
--- a/Sprint-1/refactor/includes.test.js
+++ b/Sprint-1/refactor/includes.test.js
@@ -2,6 +2,9 @@
 
 const includes = require("./includes.js");
 
+// Given an array containing the target value
+// When passed to the includes function
+// Then it should return true
 test("returns true when target is in array", () => {
   const currentOutput = includes(["a", "b", "c", "d"], "c");
   const targetOutput = true;
@@ -9,6 +12,9 @@ test("returns true when target is in array", () => {
   expect(currentOutput).toEqual(targetOutput);
 });
 
+// Given an array that does not contain the target value
+// When passed to the includes function
+// Then it should return false
 test("returns false when target not in array", () => {
   const currentOutput = includes([1, 2, 3, 4], "a");
   const targetOutput = false;
@@ -16,6 +22,9 @@ test("returns false when target not in array", () => {
   expect(currentOutput).toEqual(targetOutput);
 });
 
+// Given an array where the target appears more than once
+// When passed to the includes function
+// Then it should still return true
 test("returns true when the target is in array multiple times", () => {
   const currentOutput = includes([1, 2, 2, 3], 2);
   const targetOutput = true;
@@ -23,6 +32,9 @@ test("returns true when the target is in array multiple times", () => {
   expect(currentOutput).toEqual(targetOutput);
 });
 
+// Given an empty array
+// When passed to the includes function
+// Then it should return false
 test("returns false for empty array", () => {
   const currentOutput = includes([]);
   const targetOutput = false;
@@ -30,6 +42,9 @@ test("returns false for empty array", () => {
   expect(currentOutput).toEqual(targetOutput);
 });
 
+// Given an array containing null as an element
+// When passed to the includes function with null as the target
+// Then it should return true
 test("searches for null", () => {
   const currentOutput = includes(["b", "z", null, "a"], null);
   const targetOutput = true;