diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index b22590bc6..4507226c4 100644
--- a/Sprint-1/fix/median.js
+++ b/Sprint-1/fix/median.js
@@ -6,9 +6,35 @@
 // 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;
+  // Check that the input passed to the function is an array
+  if (!Array.isArray(list)) {
+    return null;
+  }
+
+  // Filter valid numbers and store them in `validNumbers`
+  const validNumbers = list.filter(
+    (item) => typeof item === "number" && !isNaN(item)
+  );
+
+  // Return `null` if there are no valid numbers
+  if (validNumbers.length === 0) {
+    return null;
+  }
+
+  // Sort `validNumbers` in ascending order
+  // Sort validNumbers (safe to mutate because it's a new array created by filter)
+  validNumbers.sort((a, b) => a - b);
+
+  // Calculate the middle index of the sorted array
+  const middleIndex = Math.floor(validNumbers.length / 2);
+
+  // If the array has an odd number of elements, return the middle element
+  if (validNumbers.length % 2 !== 0) {
+    return validNumbers[middleIndex];
+  } else {
+    // If the array has an even number of elements, return the average of the two middle elements
+    return (validNumbers[middleIndex - 1] + validNumbers[middleIndex]) / 2;
+  }
 }
 
 module.exports = calculateMedian;
diff --git a/Sprint-1/fix/median.test.js b/Sprint-1/fix/median.test.js
index 21da654d7..c262c3776 100644
--- a/Sprint-1/fix/median.test.js
+++ b/Sprint-1/fix/median.test.js
@@ -13,7 +13,8 @@ describe("calculateMedian", () => {
     { input: [1, 2, 3, 4], expected: 2.5 },
     { input: [1, 2, 3, 4, 5, 6], expected: 3.5 },
   ].forEach(({ input, expected }) =>
-    it(`returns the median for [${input}]`, () => expect(calculateMedian(input)).toEqual(expected))
+    it(`returns the median for [${input}]`, () =>
+      expect(calculateMedian(input)).toEqual(expected))
   );
 
   [
@@ -24,7 +25,8 @@ describe("calculateMedian", () => {
     { input: [110, 20, 0], expected: 20 },
     { input: [6, -2, 2, 12, 14], expected: 6 },
   ].forEach(({ input, expected }) =>
-    it(`returns the correct median for unsorted array [${input}]`, () => expect(calculateMedian(input)).toEqual(expected))
+    it(`returns the correct median for unsorted array [${input}]`, () =>
+      expect(calculateMedian(input)).toEqual(expected))
   );
 
   it("doesn't modify the input array [3, 1, 2]", () => {
@@ -33,8 +35,17 @@ describe("calculateMedian", () => {
     expect(list).toEqual([3, 1, 2]);
   });
 
-  [ 'not an array', 123, null, undefined, {}, [], ["apple", null, undefined] ].forEach(val =>
-    it(`returns null for non-numeric array (${val})`, () => expect(calculateMedian(val)).toBe(null))
+  [
+    "not an array",
+    123,
+    null,
+    undefined,
+    {},
+    [],
+    ["apple", null, undefined],
+  ].forEach((val) =>
+    it(`returns null for non-numeric array (${val})`, () =>
+      expect(calculateMedian(val)).toBe(null))
   );
 
   [
@@ -45,6 +56,7 @@ describe("calculateMedian", () => {
     { input: [3, "apple", 1, null, 2, undefined, 4], expected: 2.5 },
     { input: ["banana", 5, 3, "apple", 1, 4, 2], expected: 3 },
   ].forEach(({ input, expected }) =>
-    it(`filters out non-numeric values and calculates the median for [${input}]`, () => expect(calculateMedian(input)).toEqual(expected))
+    it(`filters out non-numeric values and calculates the median for [${input}]`, () =>
+      expect(calculateMedian(input)).toEqual(expected))
   );
 });
diff --git a/Sprint-1/implement/dedupe.js b/Sprint-1/implement/dedupe.js
index 781e8718a..b7372b6e7 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1 +1,43 @@
-function dedupe() {}
+// This defines a function named dedupe with a parameter arrayInput. arrayInput should be an array.
+function dedupe(arrayInput) {
+  // This checks whether the input is not an array.
+  if (!Array.isArray(arrayInput)) {
+    // If the input is not an array, the function stops, throws a TypeError and shows an error message saying:“Input must be an array.”
+    throw new TypeError("Input must be an array");
+  }
+  // This checks if the array is empty (has no elements).
+  if (arrayInput.length === 0) {
+    // If the array is empty, it returns an empty array.
+    return [];
+  }
+
+  // This declares a new variable `newArray` which will hold a reference to an empty array in memory
+  const newArray = [];
+  // This decares a new varibale `seen` which will hold a reference to the actual set object in memory
+  const seen = new Set(); // variable seen keeps track of all items that have already been added to the result array
+  // seen is a Set object that remembers items,
+
+  // newArray is an array that holds the actual result.
+
+  // This starts a loop that goes through each element in the input array one by one.
+  for (const item of arrayInput) {
+    // This big condition checks two things before adding an item:
+
+    // !seen.has(item) — The item has not been added before.
+
+    // The item is either a number (but not NaN) or a string.
+    // So only real numbers and strings that haven’t appeared yet will be kept.
+    if (
+      !seen.has(item) &&
+      ((typeof item === "number" && !Number.isNaN(item)) ||
+        typeof item === "string")
+    ) {
+      newArray.push(item); // If the item passes the condition, it gets added to the new array.
+      seen.add(item); // The item is then recorded in the Set, so it won’t be added again later.
+    }
+  }
+  // After the loop finishes, return the final deduplicated array
+  return newArray; // After checking all items, the function returns the new array with duplicates removed and invalid items filtered out.
+}
+
+module.exports = dedupe; // This line allows the dedupe function to be used in other files (like the test file).
diff --git a/Sprint-1/implement/dedupe.test.js b/Sprint-1/implement/dedupe.test.js
index 23e0f8638..41fc280d5 100644
--- a/Sprint-1/implement/dedupe.test.js
+++ b/Sprint-1/implement/dedupe.test.js
@@ -1,10 +1,11 @@
 const dedupe = require("./dedupe.js");
+
 /*
 Dedupe Array
 
-📖 Dedupe means **deduplicate**
+📖 Dedupe means **dedupe**
 
-In this kata, you will need to deduplicate the elements of an array
+In this kata, you will need to dedupe the elements of an array
 
 E.g. dedupe(['a','a','a','b','b','c']) target output: ['a','b','c']
 E.g. dedupe([5, 1, 1, 2, 3, 2, 5, 8]) target output: [5, 1, 2, 3, 8]
@@ -13,15 +14,80 @@ E.g. dedupe([1, 2, 1]) target output: [1, 2]
 
 // Acceptance Criteria:
 
-// 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");
+describe("dedupe - valid inputs", () => {
+  // Given an empty array
+  // When passed to the dedupe function
+  // Then it should return an empty array
+  [{ input: [], expected: [] }].forEach(({ input, expected }) =>
+    test(`returns an empty array for input [${input}]`, () => {
+      const result = dedupe(input);
+      expect(result).toEqual(expected);
+      expect(result).not.toBe(input); // ensures it's a new array
+    })
+  );
+
+  // Given an array with no duplicates
+  // When passed to the dedupe function
+  // Then it should return a copy of the original array
+  [
+    { input: [1, 2, 3], expected: [1, 2, 3] },
+    { input: ["a", "b", "car"], expected: ["a", "b", "car"] },
+    { input: [0, 1, 5, 6], expected: [0, 1, 5, 6] },
+  ].forEach(({ input, expected }) =>
+    test(`returns a copy of the array when no duplicates exist for input [${input}]`, () => {
+      const result = dedupe(input);
+      expect(result).toEqual(expected);
+      expect(result).not.toBe(input); // ensures it's a new array
+    })
+  );
+
+  // Given arrays with duplicates
+  [
+    { input: [5, 1, 1, 2, 3, 2, 5, 8], expected: [5, 1, 2, 3, 8] },
+    { input: [1, 1, 1, 1], expected: [1] },
+    { input: ["a", "a", "a", "b", "b", "c"], expected: ["a", "b", "c"] },
+  ].forEach(({ input, expected }) =>
+    test(`removes duplicate elements and keeps the first occurrence for [${input}]`, () => {
+      const result = dedupe(input);
+      expect(result).toEqual(expected);
+      expect(result).not.toBe(input); // ensures it's a new array
+    })
+  );
+
+  // Given arrays with numbers and strings mixed
+  [
+    { input: ["1", 1, "1", 1], expected: ["1", 1] },
+    { input: [2, "3", "hello", 5, 5], expected: [2, "3", "hello", 5] },
+  ].forEach(({ input, expected }) =>
+    test(`removes duplicates from an array of numbers and strings, keeping the first occurrence for input [${input}]`, () => {
+      const result = dedupe(input);
+      expect(result).toEqual(expected);
+      expect(result).not.toBe(input); // ensures it's a new array
+    })
+  );
+
+  // Given arrays with invalid elements
+  [
+    { input: [1, 2, true, 3, null, "a", {}], expected: [1, 2, 3, "a"] },
+    { input: ["x", undefined, "x", "y", []], expected: ["x", "y"] },
+    { input: [false, 5, 5, "hello", () => {}, 5], expected: [5, "hello"] },
+    { input: [1, NaN, 2, NaN, "hello"], expected: [1, 2, "hello"] },
+  ].forEach(({ input, expected }) =>
+    test(`filters invalid elements, removes duplicates, and returns a copy for input [${input}]`, () => {
+      const result = dedupe(input);
+      expect(result).toEqual(expected);
+      expect(result).not.toBe(input); // ensures it's a new array
+    })
+  );
+});
 
-// Given an array with no duplicates
-// When passed to the dedupe function
-// Then it should return a copy of the original array
+describe("dedupe - invalid inputs", () => {
+  const invalidInputs = [null, undefined, 123, "string", {}, () => {}];
 
-// 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
+  invalidInputs.forEach((input) =>
+    test(`throws typeError when input is ${String(input)}`, () => {
+      expect(() => dedupe(input)).toThrow(TypeError);
+      expect(() => dedupe(input)).toThrow("Input must be an array");
+    })
+  );
+});
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index 6dd76378e..0e06ebe78 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,4 +1,12 @@
 function findMax(elements) {
+  if (!Array.isArray(elements)) {
+    throw new TypeError("Input must be an array");
+  } else {
+    const filteredArray = elements.filter(
+      (ele) => typeof ele === "number" && !isNaN(ele)
+    )
+    return Math.max(...filteredArray);
+  }
 }
 
 module.exports = findMax;
diff --git a/Sprint-1/implement/max.test.js b/Sprint-1/implement/max.test.js
index 82f18fd88..8ba3d5fd3 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -16,28 +16,76 @@ 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([8])).toBe(8);
+  expect(findMax([-42])).toBe(-42);
+  expect(findMax([0])).toBe(0);
+});
 
 // 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 both positive and negative numbers, returns the largest number overall", () => {
+  expect(findMax([10, -5, 20, 0])).toBe(20);
+  expect(findMax([-1, -100, -50, 30])).toBe(30);
+  expect(findMax([0, -10, 5])).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 just negative numbers, returns the closest one to zero", () => {
+  expect(findMax([-10, -5, -20])).toBe(-5);
+  expect(findMax([-100, -50, -60])).toBe(-50);
+  expect(findMax([-1000, -60, -1])).toBe(-1);
+});
 
 // 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 number", () => {
+  expect(findMax([1.1, 2.5, 0.3])).toBe(2.5);
+  expect(findMax([-1.2, -0.5, -0.1])).toBe(-0.1);
+  expect(findMax([-1000.23, -80.54, -63.110])).toBe(-63.110);
+});
 
 // 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, returns the max and ignore the non-numeric values", () => {
+  expect(findMax([10, "hi", 20, null])).toBe(20);
+  expect(findMax([0, false, 5, "a"])).toBe(5);
+  expect(findMax([undefined, 5, null, NaN, -9])).toBe(5);
+});
 
 // 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", () => {
+  expect(findMax(["a", null, undefined])).toBe(-Infinity);
+  expect(findMax([{}, [], "hi"])).toBe(-Infinity);
+  expect(findMax([true, false, true])).toBe(-Infinity);
+  expect(findMax([Symbol("x"), () => {}, function () {}])).toBe(-Infinity);
+});
+
+// Edge cases
+// Given an array with non-array values
+// when passed to the max function
+// Then it should throw and error
+test("given a non-array input, throws a TypeError with message 'Input must be an array'", () => {
+  expect(() => findMax(42)).toThrow(new TypeError("Input must be an array"));
+  expect(() => findMax("hello")).toThrow(
+    new TypeError("Input must be an array")
+  );
+  expect(() => findMax(null)).toThrow(new TypeError("Input must be an array"));
+  expect(() => findMax(undefined)).toThrow(
+    new TypeError("Input must be an array")
+  );
+});
diff --git a/Sprint-1/implement/sum.js b/Sprint-1/implement/sum.js
index 9062aafe3..721239868 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,4 +1,16 @@
 function sum(elements) {
+  if (!Array.isArray(elements)) {
+    throw new TypeError("Input must be an array");
+  }
+  const filteredElements = elements.filter(
+    (ele) => typeof ele === "number" && !isNaN(ele)
+  );
+  let sumElements = 0;
+
+  for (const item of filteredElements) {
+    sumElements += item;
+  }
+  return sumElements;
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index dd0a090ca..dc4748e3a 100644
--- a/Sprint-1/implement/sum.test.js
+++ b/Sprint-1/implement/sum.test.js
@@ -13,24 +13,54 @@ 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);
+
+  const arr = [];
+  expect(sum(arr)).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 in an array, returns that number", () => {
+  expect(sum([5])).toBe(5);
+  expect(sum([-3])).toBe(-3);
+  expect(sum([0])).toBe(0);
+});
 
 // 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 containing negative numbers, should return the correct total sum", () => {
+  expect(sum([-5, -9, -100])).toBe(-114);
+  expect(sum([-1000, -2000, -3000])).toBe(-6000);
+  expect(sum([-1, -2, -3])).toBe(-6);
+});
 
 // 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/float numbers, should return the correct total number", () => {
+  expect(sum([-8.24, 5.46, 3.22])).toBeCloseTo(0.44);
+  expect(sum([-2.5, 2.5, 5.25])).toBeCloseTo(5.25);
+  expect(sum([1.11, 2.22, 3.33])).toBeCloseTo(6.66);
+});
 
 // 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 containing non-number values, should ignore the non-numerical values and return the sum of the numerical elements", () => {
+  expect(sum([5, -18, 5.601, null, "kettle"])).toBeCloseTo(-7.4);
+  expect(sum([true, false, 10, -5])).toBe(5);
+  expect(sum([null, 4, 6, "test"])).toBe(10);
+});
 
 // 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, should return 0", () => {
+  expect(sum(["food", null, false, true])).toBe(0);
+  expect(sum(["apple", "banana", null, undefined])).toBe(0);
+  expect(sum([NaN, NaN, NaN])).toBe(0);
+});
diff --git a/Sprint-1/refactor/includes.js b/Sprint-1/refactor/includes.js
index 29dad81f0..6aeac0b5d 100644
--- a/Sprint-1/refactor/includes.js
+++ b/Sprint-1/refactor/includes.js
@@ -1,9 +1,8 @@
 // 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];
-    if (element === target) {
+  for (const item of list) {
+    if (item === target) {
       return true;
     }
   }
diff --git a/prep/mean-median.js b/prep/mean-median.js
new file mode 100644
index 000000000..c79e65573
--- /dev/null
+++ b/prep/mean-median.js
@@ -0,0 +1,53 @@
+function calculateMean(list) {
+  let total = 0;
+
+  for (const item of list) {
+    total += item;
+  }
+  console.log("the total of the array is", total);
+  console.log("the element has",list.length, "elements");
+  return (total/list.length);
+  
+}
+
+function calculateMedian(list) {
+  const middleIndex = Math.floor(list.length / 2);
+  const median = list.splice(middleIndex, 1)[0]; // Because the splice method has been used on the variable list, 
+  // the array stored in memory will change, and any variable that points to it will show the updated array.
+
+  return median;
+}
+
+const salaries = [10, 20, 30, 40, 60, 80, 80]; 
+const median = calculateMedian(salaries);
+
+console.log(salaries, "<--- salaries input before we call calculateMean");
+const mean = calculateMean(salaries);
+
+console.log(`The median of the salaries is ${median}`);
+console.log(`The mean of the salaries is ${mean}`);
+console.log(salaries);
+
+// Notes to understand Array as a reference type
+// 1. Arrays are reference types
+
+// This means that when you create an array like this:
+// const salaries = [10, 20, 30, 40, 60, 80, 80];
+// JavaScript doesn’t store the array itself directly in the variable salaries.
+
+// Instead, the array is stored somewhere in memory, and salaries holds a reference (or pointer) to that memory location.
+// 2. What “reference” means
+
+// Think of it like this: the array is a house, and salaries is the address of that house.
+
+// If you write:
+// const other = salaries;
+// now other has the same address. Both salaries and other point to the same array in memory.
+
+// 3. Implication: modifying the array
+
+// Because both variables point to the same array, changing it through one variable affects the other:
+// other[0] = 100;
+// console.log(salaries[0]); // 100
+// This happens because there is only one array in memory, and both variables reference it.
+
diff --git a/prep/mean.js b/prep/mean.js
new file mode 100644
index 000000000..de9d6f4d7
--- /dev/null
+++ b/prep/mean.js
@@ -0,0 +1,14 @@
+function calculateMean(list) {
+    let total = 0;
+     
+    for (const item of list) {
+        total += item;
+    }
+    console.log("the total of the array is", total);
+    console.log("the element has", list.length, "elements");
+    return total / list.length;
+}
+
+//calculateMean([1,2,3,4,5]);
+
+module.exports = calculateMean;
\ No newline at end of file
diff --git a/prep/mean.test.js b/prep/mean.test.js
new file mode 100644
index 000000000..4123bf07e
--- /dev/null
+++ b/prep/mean.test.js
@@ -0,0 +1,9 @@
+const calculateMean = require("./mean");
+
+test("Calculate the average of a list of numbers", () => {
+  const list = [3, 50, 7];
+  const currentOutput = calculateMean(list);
+  const targetOutput = 20; // 20 is (3 + 50 + 7) / 3
+  
+  expect(currentOutput).toEqual(targetOutput);
+});
diff --git a/prep/median.js b/prep/median.js
new file mode 100644
index 000000000..d008917bb
--- /dev/null
+++ b/prep/median.js
@@ -0,0 +1,31 @@
+// How to calculate the median of an array by mutating the array
+
+// function calculateMedian(list) {
+//   const middleIndex = Math.floor(list.length / 2);
+//   const median = list.splice(middleIndex, 1)[0];
+//   console.log("middleIndex", middleIndex);
+//   console.log(list);
+//   return median;
+// }
+
+// const actualOutput = calculateMedian([1, 2, 3]);
+// console.log("median", actualOutput);
+module.exports = calculateMedian;
+
+// How to calculate the median of an array without muatating the array
+function calculateMedian(list) {
+  let medianIndex;
+  let actualMedian;
+  const arrayLength = list.length; // 3
+  if (arrayLength % 2 !== 0) {
+    medianIndex = (arrayLength + 1) / 2;
+    actualMedian = list[medianIndex - 1];
+  } else {
+    medianIndex = arrayLength / 2;
+
+    firstMedianIndex = list[medianIndex - 1];
+    secondMedianIndex = list[medianIndex];
+    actualMedian = (firstMedianIndex + secondMedianIndex) / 2;
+  }
+  return actualMedian;
+}
diff --git a/prep/median.test.js b/prep/median.test.js
new file mode 100644
index 000000000..b0ed64d2d
--- /dev/null
+++ b/prep/median.test.js
@@ -0,0 +1,24 @@
+const calculateMedian = require("./median");
+
+test("Calculate the median of the list of numbers", () => {
+  const list = [10, 20, 30, 40, 50];
+  const currentOutput = calculateMedian(list);
+  const targetOutput = 30;
+
+  expect(currentOutput).toEqual(targetOutput);
+});
+
+test("should not modify the input", () => {
+  const list = [1, 2, 3];
+  const currentOutput = calculateMedian(list);
+
+  expect(currentOutput).toEqual(2);
+});
+
+test("should return the average of the two middle numbers as the median for an array with even length", () => {
+    const list = [2, 6, 4, 3];
+    const currentOutput = calculateMedian(list);
+    expect(currentOutput).toEqual(5)
+  }
+);
+
diff --git a/prep/package.json b/prep/package.json
new file mode 100644
index 000000000..8cf1fc5ab
--- /dev/null
+++ b/prep/package.json
@@ -0,0 +1,13 @@
+{
+  "devDependencies": {
+    "jest": "^30.2.0"
+  },
+  "scripts": {
+    "test": "jest"
+  }
+}
+
+
+  
+
+