diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index 5c5b796e1..8bf6aa764 100644
--- a/Sprint-1/fix/median.js
+++ b/Sprint-1/fix/median.js
@@ -6,9 +6,25 @@
 // or contains values that aren't numbers (the function is expected to throw - see the tests).
 
 function calculateMedian(list) {
-  const middleIndex = Math.floor(list.length / 2);
-  const median = list.splice(middleIndex, 1)[0];
-  return median;
+  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");
+  }
+
+  for (const item of list) {
+    if (typeof item !== "number") {
+      throw new Error("calculateMedian requires an array of numbers");
+    }
+  }
+  const sorted = [...list].sort((a, b) => a - b);
+  const middleIndex = Math.floor(sorted.length / 2);
+  if (sorted.length % 2 === 0) {
+    return (sorted[middleIndex - 1] + sorted[middleIndex]) / 2;
+  }
+  return sorted[middleIndex];
 }
 
 module.exports = calculateMedian;
diff --git a/Sprint-1/implement/dedupe.js b/Sprint-1/implement/dedupe.js
index 781e8718a..2ec3c6352 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1 +1,16 @@
-function dedupe() {}
+function dedupe(list) {
+  const elements = [];
+
+  if (list.length === 0) {
+    return [];
+  }
+
+  for (const item of list) {
+    if (!elements.includes(item)) {
+      elements.push(item);
+    }
+  }
+  return elements;
+}
+
+module.exports = dedupe;
diff --git a/Sprint-1/implement/dedupe.test.js b/Sprint-1/implement/dedupe.test.js
index d7c8e3d8e..094e7dc0c 100644
--- a/Sprint-1/implement/dedupe.test.js
+++ b/Sprint-1/implement/dedupe.test.js
@@ -16,13 +16,27 @@ 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", () => {
+  const list = [];
+  const result = dedupe(list);
+  expect(dedupe(list)).toEqual(result);
+});
 
 // 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 list = ["a", "b", "c"];
+  const result = dedupe(list);
+  expect(dedupe(list)).toEqual(result);
+});
 
 // 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, it returns an array with duplicates removed and its original occurrence", () => {
+  const list = [3, 1, 2];
+  const result = dedupe(list);
+  expect(dedupe(list)).toEqual(result);
+});
diff --git a/Sprint-1/implement/describe-median.js b/Sprint-1/implement/describe-median.js
index 3381cfc0a..e81890647 100644
--- a/Sprint-1/implement/describe-median.js
+++ b/Sprint-1/implement/describe-median.js
@@ -20,6 +20,12 @@ function calculateMedian(list) {
 }
 
 // Implement this function. See describe-median.test.js for the acceptance criteria.
-function describeMedian(list) {}
+function describeMedian(list) {
+  try {
+    return `The median is ${calculateMedian(list)}`;
+  } catch (error) {
+    return `Could not calculate a median: calculateMedian requires a non-empty array: ${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..49427757d 100644
--- a/Sprint-1/implement/describe-median.test.js
+++ b/Sprint-1/implement/describe-median.test.js
@@ -15,18 +15,33 @@ message, so the caller can see what went wrong.
 
 const describeMedian = require("./describe-median.js");
 
+
 // Acceptance criteria:
 
 // Given an array of numbers
 // 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", () => {
+    const list = [1, 2, 3];
+    const result = describeMedian(list);
+    expect(describeMedian(list)).toEqual(result);
+});
 
 // 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 an empty array [], returns Could not calculate a median", () => {
+  const list = [];
+  const result = describeMedian(list);
+  expect(describeMedian(list)).toEqual(result);
+});
 
 // 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 a non-array , returns Could not calculate a median", () => {
+  const list = [];
+  const result = describeMedian(list);
+  expect(describeMedian(list)).toEqual(result);
+});
\ No newline at end of file
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index 6dd76378e..efee75da5 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,4 +1,18 @@
 function findMax(elements) {
+  if (!Array.isArray(elements)) {
+    throw new Error("findMax requires an array of numbers");
+  }
+
+  for (const element of elements) {
+    if (typeof element !== "number") {
+      throw new Error("findMax requires an array of numbers");
+    }
+
+    if (!elements.length === 1) {
+      return element;
+    }
+  }
+  return Math.max(...elements);
 }
 
 module.exports = findMax;
diff --git a/Sprint-1/implement/max.test.js b/Sprint-1/implement/max.test.js
index ff3fbb5e5..2fbfa0139 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -16,28 +16,60 @@ 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", () => {
+  const list = [1];
+  const result = findMax(list);
+  expect(result).toEqual(1);
+});
 
 // 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 number", () => {
+  const list = [1, -9, 7, -5];
+  const result = findMax(list);
+  expect(result).toEqual(7);
+});
 
 // 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 negative numbers, returns closest one to zero", () => {
+  const list = [-1, -9, -7, -5];
+  const result = findMax(list);
+  expect(result).toEqual(-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", () => {
+  const list = [1.1, 0.9, 4.7, 1.5];
+  const result = findMax(list);
+  expect(result).toEqual(4.7);
+});
 
 // 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("given an array with non-numbers, returns, findMax requires an array of numbers", () => {
+  expect(() => findMax(["a", "l", "k"])).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("given a non-array, returns, findMax requires an array of numbers", () => {
+  expect(() => findMax("a", "", 7, "kilo")).toThrow(
+    new Error("findMax requires an array of numbers")
+  );
+});
\ No newline at end of file
diff --git a/Sprint-1/implement/mean.js b/Sprint-1/implement/mean.js
index 36909ea1f..fbbecbddd 100644
--- a/Sprint-1/implement/mean.js
+++ b/Sprint-1/implement/mean.js
@@ -1,3 +1,18 @@
-function calculateMean(list) {}
+function calculateMean(list) {
+  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 item of list) {
+    if (typeof item !== "number") {
+      throw new Error("calculateMean requires an array of numbers");
+    }
+    total = total + item;
+  }
+  return Number(total.toFixed(2)) / list.length;
+}
 module.exports = calculateMean;
diff --git a/Sprint-1/implement/mean.test.js b/Sprint-1/implement/mean.test.js
index 847b88676..ee7e93f8f 100644
--- a/Sprint-1/implement/mean.test.js
+++ b/Sprint-1/implement/mean.test.js
@@ -23,28 +23,66 @@ 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", () => {
+  const list = [1, 2, 6];
+  const result = calculateMean(list);
+  expect(result).toEqual(3);
+});
 
 // Given an array with a single number
 // When passed to calculateMean
 // Then it should return that number
+test("given [6], returns 6", () => {
+  expect(6).toEqual(6);
+});
 
 // Given an array containing negative or decimal numbers
 // When passed to calculateMean
 // Then it should return the correct mean
+test("given negative numbers, return mean", () => {
+  const list = [-7, -3, -5];
+  const result = calculateMean(list);
+  expect(result).toEqual(-5);
+});
+
+  test("given decimal numbers, return mean", () => {
+  const list = [7.2, 2.4, 6.8];
+  const result = calculateMean(list);
+  expect(result).toBeCloseTo(5.47);
+});
 
 // Given an empty array
 // When passed to calculateMean
 // Then it should throw Error("calculateMean requires a non-empty array")
+test("given an empty array, returns, calculateMean requires a non-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("given a non-array, returns, calculateMean requires an array of numbers", () => {
+  expect(() => calculateMean("banana", 42, null, {})).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("given no argument, returns, calculateMean requires an array of numbers", () => {
+  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("given non-number containing array, returns, calculateMean requires an array of numbers", () => {
+  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..f5ccb538b 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,4 +1,15 @@
 function sum(elements) {
+  if (!Array.isArray(elements)) {
+    throw new Error("sum requires an array of numbers");
+  }
+  let total = 0;
+  for (const element of elements) {
+    if (typeof element !== "number") {
+      throw new Error("sum requires an array of numbers");
+    }
+    total += element;
+  }
+  return Number(total.toFixed(2));
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index a288e0f0a..172daac6d 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 a one number array, returns the same number", () => {
+  expect(sum([9])).toEqual(9);
+});
 
 // Given an array containing negative numbers
 // When passed to the sum function
 // Then it should still return the correct total sum
+test("given a negative number array, returns the sum", () => {
+  expect(sum([-9, -3, -6])).toEqual(-18);
+});
 
 // Given an array with decimal/float numbers
 // When passed to the sum function
 // Then it should return the correct total sum
+test("given a decimal numbers array, returns the sum", () => {
+  expect(sum([1.9, 7.5, 4.91])).toBeCloseTo(14.31);
+});
 
 // 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("given a non-numbers array, returns sum requires an array of numbers", () => {
+  expect(() => sum(["apple", null ,3])).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("given a non-array, returns sum requires an array of numbers", () => {
+  expect(() => sum("apple", null, 3)).toThrow(
+    new Error("sum requires an array of numbers")
+  );
+});
\ No newline at end of file
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-1/stretch/aoc-2018-day1/solution.js b/Sprint-1/stretch/aoc-2018-day1/solution.js
index e69de29bb..c746c509c 100644
--- a/Sprint-1/stretch/aoc-2018-day1/solution.js
+++ b/Sprint-1/stretch/aoc-2018-day1/solution.js
@@ -0,0 +1,14 @@
+const fs = require("fs");
+const inputText = fs.readFileSync("input.txt", "utf8");
+
+function calculateResultingFrequency(frequencyChangeLines) {
+  const lines = frequencyChangeLines.split("\n");
+  const frequencyChangeAsNumbers = lines.map((change) => Number(change));
+  let resultingFrequency = 0;
+
+  for (const frequencyChange of frequencyChangeAsNumbers) {
+    resultingFrequency += frequencyChange;
+  }
+  return resultingFrequency;
+}
+console.log(calculateResultingFrequency(inputText));