diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index 5c5b796e1..4cbaa1d2d 100644
--- a/Sprint-1/fix/median.js
+++ b/Sprint-1/fix/median.js
@@ -6,8 +6,27 @@
 // or contains values that aren't numbers (the function is expected to throw - see the tests).
 
 function calculateMedian(list) {
+  if (!Array.isArray(list)) {
+    throw new Error("calculateMedian requires an array of numbers");
+  }
+  if (list.length === 0) {
+    throw new Error("calculateMedian requires a non-empty array");
+  }
   const middleIndex = Math.floor(list.length / 2);
-  const median = list.splice(middleIndex, 1)[0];
+  let median;
+  const copyList = list.slice();
+  copyList.sort((a, b) => a - b);
+
+  for (const elements of copyList) {
+    if (typeof elements !== "number") {
+      throw new Error("calculateMedian requires an array of numbers");
+    }
+  }
+  if (copyList.length % 2 === 0) {
+    median = (copyList[middleIndex] + copyList[middleIndex - 1]) / 2;
+  } else {
+    median = copyList[middleIndex];
+  }
   return median;
 }
 
diff --git a/Sprint-1/implement/dedupe.js b/Sprint-1/implement/dedupe.js
index 781e8718a..0af9cf74b 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1 +1,14 @@
-function dedupe() {}
+function dedupe(elements) {
+  if (elements.length === 0) {
+    return [];
+  }
+  let newArray = [];
+  for (const items of elements) {
+    if (!newArray.includes(items)) {
+      newArray.push(items);
+    }
+  }
+  return newArray;
+}
+
+module.exports = dedupe;
diff --git a/Sprint-1/implement/dedupe.test.js b/Sprint-1/implement/dedupe.test.js
index d7c8e3d8e..47c833a08 100644
--- a/Sprint-1/implement/dedupe.test.js
+++ b/Sprint-1/implement/dedupe.test.js
@@ -16,13 +16,26 @@ E.g. dedupe([1, 2, 1]) returns [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 copy of original array", () => {
+  expect(dedupe([1, 2, 3, 4])).toEqual([1, 2, 3, 4]);
+});
 
 // Given an array of strings or numbers
 // When passed to the dedupe function
-// Then it should return a new array with duplicates removed while preserving the 
+// Then it should return a new array with duplicates removed while preserving the
 // first occurrence of each element from the original array.
+test("given an array with duplicates of strings and numbers it returns first occurrence of each element", () => {
+  expect(dedupe([1, "ball", "ball", 3, 1, "egg"])).toEqual([
+    1,
+    "ball",
+    3,
+    "egg",
+  ]);
+});
diff --git a/Sprint-1/implement/describe-median.js b/Sprint-1/implement/describe-median.js
index 3381cfc0a..13c77d4ce 100644
--- a/Sprint-1/implement/describe-median.js
+++ b/Sprint-1/implement/describe-median.js
@@ -20,6 +20,18 @@ function calculateMedian(list) {
 }
 
 // Implement this function. See describe-median.test.js for the acceptance criteria.
-function describeMedian(list) {}
+function describeMedian(list) {
+  try {
+    const median = calculateMedian(list);
+    return `The median is ${median}`;
+  } catch (error) {
+    if (error.message === "calculateMedian requires a non-empty array") {
+      return `Could not calculate a median: ${error.message}`;
+    }
+    if (error.message === "calculateMedian requires an array of numbers") {
+      return `Could not calculate a median: ${error.message}`;
+    }
+  }
+}
 
 module.exports = describeMedian;
diff --git a/Sprint-1/implement/describe-median.test.js b/Sprint-1/implement/describe-median.test.js
index e7d18a264..4f2b9ed62 100644
--- a/Sprint-1/implement/describe-median.test.js
+++ b/Sprint-1/implement/describe-median.test.js
@@ -21,12 +21,24 @@ const describeMedian = require("./describe-median.js");
 // When passed to describeMedian
 // Then it should return "The median is " followed by the median
 // Delete this test.todo and replace it with a test.
-test.todo('given [1, 2, 3], returns "The median is 2"');
+test('given [1, 2, 3], returns "The median is 2"', () => {
+  expect(describeMedian([1, 2, 3])).toEqual("The median is 2");
+});
 
 // Given an empty array
 // When passed to describeMedian
 // Then it should return "Could not calculate a median: calculateMedian requires a non-empty array"
+test('given [], returns "Could not calculate a median: calculateMedian requires a non-empty array"', () => {
+  expect(describeMedian([])).toEqual(
+    "Could not calculate a median: calculateMedian requires a non-empty array"
+  );
+});
 
 // Given something that isn't an array of numbers, e.g. "banana"
 // When passed to describeMedian
 // Then it should return "Could not calculate a median: calculateMedian requires an array of numbers"
+test('given not an array, returns "Could not calculate a median: calculateMedian requires an array of numbers"', () => {
+  expect(describeMedian("banana")).toEqual(
+    "Could not calculate a median: calculateMedian requires an array of numbers"
+  );
+});
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index 6dd76378e..c143005c5 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,4 +1,25 @@
 function findMax(elements) {
+  if (!Array.isArray(elements)) {
+    throw new Error("findMax requires an array of numbers");
+  }
+  for (const items of elements) {
+    if (typeof items !== "number") {
+      throw new Error("findMax requires an array of numbers");
+    }
+  }
+  if (elements.length === 0) {
+    return -Infinity;
+  }
+  if (elements.length === 1) {
+    return elements[0];
+  }
+  let max = elements[0];
+  for (const items of elements) {
+    if (items > max) {
+      max = items;
+    }
+  }
+  return max;
 }
 
 module.exports = findMax;
diff --git a/Sprint-1/implement/max.test.js b/Sprint-1/implement/max.test.js
index ff3fbb5e5..5984fd905 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -16,28 +16,52 @@ 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 one element number in an array, returns that number", () => {
+  expect(findMax([23])).toEqual(23);
+});
 
 // Given an array with both positive and negative numbers
 // When passed to the max function
 // Then it should return the largest number overall
+test("returns the largest number in an array", () => {
+  expect(findMax([2, -4, 0, -3, 5])).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("returns the closest number to zero in an array", () => {
+  expect(findMax([-22, -4, -2, -3, -5])).toEqual(-2);
+});
 
 // Given an array with decimal numbers
 // When passed to the max function
 // Then it should return the largest decimal number
+test("returns the largest decimal number in an array", () => {
+  expect(findMax([0.34, 6.3, 2.2, 7.1, 5.0])).toEqual(7.1);
+});
 
 // Given an array containing a value that isn't a number
 // When passed to the max function
 // Then it should throw Error("findMax requires an array of numbers")
+test("throws for an array mixing numbers and strings", () => {
+  expect(() => findMax([2, -4, "hi", -3, 5])).toThrow(
+    new Error("findMax requires an array of numbers")
+  );
+});
 
 // Given something that isn't an array at all, such as "hey", 42 or no argument
 // When passed to the max function
 // Then it should throw Error("findMax requires an array of numbers")
+test("throws when not given an array type", () => {
+  expect(() => findMax("hey")).toThrow(
+    new Error("findMax requires an array of numbers")
+  );
+});
diff --git a/Sprint-1/implement/mean.js b/Sprint-1/implement/mean.js
index 36909ea1f..b35e852b4 100644
--- a/Sprint-1/implement/mean.js
+++ b/Sprint-1/implement/mean.js
@@ -1,3 +1,21 @@
-function calculateMean(list) {}
+function calculateMean(list) {
+  if (list === undefined) {
+    throw new Error("calculateMean requires an array of numbers");
+  }
+  if (!Array.isArray(list)) {
+    throw new Error("calculateMean requires an array of numbers");
+  }
+  if (list.length === 0) {
+    throw new Error("calculateMean requires a non-empty array");
+  }
+  let total = 0;
+  for (const elements of list) {
+    if (typeof elements !== "number") {
+      throw new Error("calculateMean requires an array of numbers");
+    }
+    total = total + elements;
+  }
+  return total / list.length;
+}
 
 module.exports = calculateMean;
diff --git a/Sprint-1/implement/mean.test.js b/Sprint-1/implement/mean.test.js
index 847b88676..007aa7ade 100644
--- a/Sprint-1/implement/mean.test.js
+++ b/Sprint-1/implement/mean.test.js
@@ -23,28 +23,56 @@ const calculateMean = require("./mean.js");
 // When passed to calculateMean
 // Then it should return their mean
 // Delete this test.todo and replace it with a test.
-test.todo("given [1, 2, 6], returns 3");
+test("given [1, 2, 6], returns 3", () => {
+  expect(calculateMean([1, 2, 6])).toEqual(3);
+});
 
 // Given an array with a single number
 // When passed to calculateMean
 // Then it should return that number
+test("given [1], returns 1", () => {
+  expect(calculateMean([1])).toEqual(1);
+});
 
 // Given an array containing negative or decimal numbers
 // When passed to calculateMean
 // Then it should return the correct mean
+test("given [1, 2, 6], returns 3", () => {
+  expect(calculateMean([-2, 2.8, 4.6])).toBeCloseTo(1.8);
+});
 
 // Given an empty array
 // When passed to calculateMean
 // Then it should throw Error("calculateMean requires a non-empty array")
+test("throws an error when given empty array", () => {
+  expect(() => {
+    calculateMean([]);
+  }).toThrow(new Error("calculateMean requires a non-empty array"));
+});
 
 // Given a value that isn't an array, e.g. "banana", 42, null or {}
 // When passed to calculateMean
 // Then it should throw Error("calculateMean requires an array of numbers")
+test("throws an error when not given an array", () => {
+  expect(() => {
+    calculateMean("hello");
+  }).toThrow(new Error("calculateMean requires an array of numbers"));
+});
 
 // Given no argument at all
 // When passed to calculateMean
 // Then it should throw Error("calculateMean requires an array of numbers")
+test("throws an error when no argument is given", () => {
+  expect(() => {
+    calculateMean();
+  }).toThrow(new Error("calculateMean requires an array of numbers"));
+});
 
 // Given an array containing a non-number value, e.g. [1, "2", 3]
 // When passed to calculateMean
 // Then it should throw Error("calculateMean requires an array of numbers")
+test("throws an error when an array contains non-number values", () => {
+  expect(() => {
+    calculateMean([1, "2", 3]);
+  }).toThrow(new Error("calculateMean requires an array of numbers"));
+});
diff --git a/Sprint-1/implement/sum.js b/Sprint-1/implement/sum.js
index 9062aafe3..8bbe73f1a 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,4 +1,21 @@
 function sum(elements) {
+  if (!Array.isArray(elements)) {
+    throw new Error("sum requires an array of numbers");
+  }
+  for (const items of elements) {
+    if (typeof items !== "number") {
+      throw new Error("sum requires an array of numbers");
+    }
+  }
+  if (elements.length === 0) {
+    return 0;
+  }
+
+  let sum = 0;
+  for (const items of elements) {
+    sum = sum + items;
+  }
+  return sum;
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index a288e0f0a..ff9926eed 100644
--- a/Sprint-1/implement/sum.test.js
+++ b/Sprint-1/implement/sum.test.js
@@ -13,24 +13,45 @@ 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 one element in an array, returns that number", () => {
+  expect(sum([7])).toEqual(7);
+});
 
 // Given an array containing negative numbers
 // When passed to the sum function
 // Then it should still return the correct total sum
+test("given negative elements in an array, returns sum of negative numbers", () => {
+  expect(sum([-1, -4, -7, -3])).toEqual(-15);
+});
 
 // Given an array with decimal/float numbers
 // When passed to the sum function
 // Then it should return the correct total sum
+test("given decimal elements in an array, returns sum of decimal numbers", () => {
+  expect(sum([1.0, 4.4, 2.7, 0.6])).toBeCloseTo(8.7);
+});
 
 // Given an array containing a value that isn't a number
 // When passed to the sum function
 // Then it should throw Error("sum requires an array of numbers")
+test("throws error when elements of an array are not numbers", () => {
+  expect(() => {
+    sum(["hi", 7, "hello", "10"]);
+  }).toThrow(new Error("sum requires an array of numbers"));
+});
 
 // Given something that isn't an array at all, such as "hey", 42 or no argument
 // When passed to the sum function
 // Then it should throw Error("sum requires an array of numbers")
+test("throws error when parameter is not an array", () => {
+  expect(() => {
+    sum("hello");
+  }).toThrow(new Error("sum requires an array of numbers"));
+});
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;
     }