diff --git a/Sprint-1/fix/median.js b/Sprint-1/fix/median.js
index b22590bc6..44fafde53 100644
--- a/Sprint-1/fix/median.js
+++ b/Sprint-1/fix/median.js
@@ -6,9 +6,26 @@
 // 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;
+  if (!Array.isArray(list)) {
+    return null;
+  }
+
+  const numbers = list.filter(
+    (value) => typeof value === "number" && !Number.isNaN(value)
+  );
+
+  if (numbers.length === 0) {
+    return null;
+  }
+
+  const sorted = [...numbers].sort((a, b) => a - b);
+  const middle = Math.floor(sorted.length / 2);
+
+  if (sorted.length % 2 === 0) {
+    return (sorted[middle - 1] + sorted[middle]) / 2;
+  }
+
+  return sorted[middle];
 }
 
 module.exports = calculateMedian;
diff --git a/Sprint-1/implement/dedupe.js b/Sprint-1/implement/dedupe.js
index 781e8718a..298230541 100644
--- a/Sprint-1/implement/dedupe.js
+++ b/Sprint-1/implement/dedupe.js
@@ -1 +1,5 @@
-function dedupe() {}
+function dedupe(array) {
+  return [...new Set(array)];
+}
+
+module.exports = dedupe;
diff --git a/Sprint-1/implement/dedupe.test.js b/Sprint-1/implement/dedupe.test.js
index d7c8e3d8e..bf09dded0 100644
--- a/Sprint-1/implement/dedupe.test.js
+++ b/Sprint-1/implement/dedupe.test.js
@@ -1,4 +1,5 @@
 const dedupe = require("./dedupe.js");
+
 /*
 Dedupe Array
 
@@ -16,13 +17,33 @@ 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 a copy of the original array", () => {
+  const input = [1, 2, 3];
+  const result = dedupe(input);
+
+  expect(result).toEqual([1, 2, 3]);
+  expect(result).not.toBe(input);
+});
 
 // 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("removes duplicate strings", () => {
+  expect(dedupe(["a", "a", "a", "b", "b", "c"])).toEqual(["a", "b", "c"]);
+});
+
+test("removes duplicate numbers", () => {
+  expect(dedupe([5, 1, 1, 2, 3, 2, 5, 8])).toEqual([5, 1, 2, 3, 8]);
+});
+
+test("preserves the first occurrence of each element", () => {
+  expect(dedupe([1, 2, 1])).toEqual([1, 2]);
+});
diff --git a/Sprint-1/implement/max.js b/Sprint-1/implement/max.js
index 6dd76378e..ce2e01849 100644
--- a/Sprint-1/implement/max.js
+++ b/Sprint-1/implement/max.js
@@ -1,4 +1,9 @@
 function findMax(elements) {
+  const numbers = elements.filter(
+    (element) => typeof element === "number" && !Number.isNaN(element)
+  );
+
+  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..75a1e7cc9 100644
--- a/Sprint-1/implement/max.test.js
+++ b/Sprint-1/implement/max.test.js
@@ -15,29 +15,48 @@ const findMax = require("./max.js");
 // Given an empty array
 // 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([5])).toBe(5);
+});
 
 // 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 from positive and negative numbers", () => {
+  expect(findMax([-10, 20, -5, 15])).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("returns the largest negative number", () => {
+  expect(findMax([-10, -5, -20])).toBe(-5);
+});
 
 // 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", () => {
+  expect(findMax([1.5, 2.7, 2.3])).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-number values", () => {
+  expect(findMax(["hey", 10, "hi", 60, 10])).toBe(60);
+});
 
 // 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("returns -Infinity when the array contains only non-number values", () => {
+  expect(findMax(["hey", null, undefined, "hi"])).toBe(-Infinity);
+});
diff --git a/Sprint-1/implement/sum.js b/Sprint-1/implement/sum.js
index 9062aafe3..310a81da0 100644
--- a/Sprint-1/implement/sum.js
+++ b/Sprint-1/implement/sum.js
@@ -1,4 +1,7 @@
 function sum(elements) {
+  return elements
+    .filter((element) => typeof element === "number" && !Number.isNaN(element))
+    .reduce((total, number) => total + number, 0);
 }
 
 module.exports = sum;
diff --git a/Sprint-1/implement/sum.test.js b/Sprint-1/implement/sum.test.js
index dd0a090ca..63fbd6c37 100644
--- a/Sprint-1/implement/sum.test.js
+++ b/Sprint-1/implement/sum.test.js
@@ -8,29 +8,44 @@ E.g. sum(['hey', 10, 'hi', 60, 10]), target output: 80 (ignore any non-numerical
 
 const sum = require("./sum.js");
 
-// Acceptance Criteria:
-
 // 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 an array with one number, returns that number", () => {
+  expect(sum([5])).toBe(5);
+});
 
 // Given an array containing negative numbers
 // When passed to the sum function
 // Then it should still return the correct total sum
+test("returns the correct sum for negative numbers", () => {
+  expect(sum([-5, 10, -2])).toBe(3);
+});
 
 // Given an array with decimal/float numbers
 // When passed to the sum function
 // Then it should return the correct total sum
+test("returns the correct sum for decimal numbers", () => {
+  expect(sum([1.5, 2.5, 3])).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", () => {
+  expect(sum(["hey", 10, "hi", 60, 10])).toBe(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("returns 0 when there are only non-number values", () => {
+  expect(sum(["hey", null, undefined, "hi"])).toBe(0);
+});
diff --git a/Sprint-1/refactor/includes.js b/Sprint-1/refactor/includes.js
index 29dad81f0..802cb86af 100644
--- a/Sprint-1/refactor/includes.js
+++ b/Sprint-1/refactor/includes.js
@@ -1,12 +1,12 @@
 // 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;
     }
   }
+
   return false;
 }
 
diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..00c16466e 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+//code won't work because it's looking for the house number in the wrong place
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +12,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..5b6ea1e48 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+//will give an error because author is an object, and you can't use a for...of loop directly on an object
 // This program attempts to log out all the property values in the object.
 // But it isn't working. Explain why first and then fix the problem
 
@@ -11,6 +11,6 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value of Object.values(author)) {
   console.log(value);
 }
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..faa715f1d 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,5 +1,5 @@
 // Predict and explain first...
-
+//it won't print the ingredients properly because recipe is an object
 // This program should log out the title, how many it serves and the ingredients.
 // Each ingredient should be logged on a new line
 // How can you fix it?
@@ -11,5 +11,4 @@ const recipe = {
 };
 
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+Ingredients:${recipe.ingredients.join("\n")}`);
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..67bad14f5 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,9 @@
-function contains() {}
+function contains(object, property) {
+  if (typeof object !== "object" || object === null || Array.isArray(object)) {
+    return false;
+  }
+
+  return object.hasOwnProperty(property);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..798b9ccb8 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -8,28 +8,35 @@ E.g. contains({a: 1, b: 2}, 'a') // returns true
 as the object contains a key of 'a'
 
 E.g. contains({a: 1, b: 2}, 'c') // returns false
-as the object doesn't contains a key of 'c'
+as the object doesn't contain a key of 'c'
 */
 
 // Acceptance criteria:
 
-// Given a contains function
-// When passed an object and a property name
-// Then it should return true if the object contains the property, false otherwise
-
 // Given an empty object
 // When passed to contains
 // Then it should return false
-test.todo("contains on empty object returns false");
+test("contains on empty object returns false", () => {
+  expect(contains({}, "a")).toBe(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("contains returns true when property exists", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("contains returns false when property does not exist", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("contains returns false when passed an array", () => {
+  expect(contains([], "length")).toBe(false);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..e87f9c05d 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,14 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  const lookup = {};
+
+  for (const pair of countryCurrencyPairs) {
+    const countryCode = pair[0];
+    const currencyCode = pair[1];
+
+    lookup[countryCode] = currencyCode;
+  }
+
+  return lookup;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..d5cb19e63 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -33,3 +33,14 @@ It should return:
    'CA': 'CAD'
  }
 */
+test("creates a country currency code lookup for multiple codes", () => {
+  const countryCurrencyPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+  ];
+
+  expect(createLookup(countryCurrencyPairs)).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..1b287f1c3 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,13 +1,47 @@
 function parseQueryString(queryString) {
   const queryParams = {};
+
+  if (queryString === null || queryString === undefined) {
+    return queryParams;
+  }
+
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    // Ignore empty pairs
+    if (pair === "") {
+      continue;
+    }
+
+    // Split only on the first "="
+    const [keyPart, ...valueParts] = pair.split("=");
+
+    let key = keyPart;
+    let value = valueParts.join("=");
+
+    // If there is no "=" the value should be empty
+    if (valueParts.length === 0) {
+      value = "";
+    }
+
+    // Replace + with spaces and decode URL encoding
+    key = decodeURIComponent(key.replace(/\+/g, " "));
+    value = decodeURIComponent(value.replace(/\+/g, " "));
+
+    // Handle duplicate keys
+    if (Object.prototype.hasOwnProperty.call(queryParams, key)) {
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    } else {
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..b468ef9d1 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -3,7 +3,7 @@
 // Below are some test cases the implementation doesn't handle well.
 // Fix the implementation for these tests, and try to think of as many other edge cases as possible - write tests and fix those too.
 
-const parseQueryString = require("./querystring.js")
+const parseQueryString = require("./querystring.js");
 
 test("should parse values containing '='", () => {
   expect(parseQueryString("equation=a=b-2")).toEqual({
@@ -46,3 +46,37 @@ test("should store values of a key in an array when the key has 2 or more values
     foo: "bar",
   });
 });
+
+test("should return an empty object for an empty query string", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("should handle values containing multiple equals signs", () => {
+  expect(parseQueryString("url=a=b=c")).toEqual({
+    url: "a=b=c",
+  });
+});
+
+test("should ignore multiple empty pairs", () => {
+  expect(parseQueryString("&&foo=bar&&")).toEqual({
+    foo: "bar",
+  });
+});
+
+test("should decode spaces using percent encoding", () => {
+  expect(parseQueryString("name=John%20Doe")).toEqual({
+    name: "John Doe",
+  });
+});
+
+test("should handle empty values with duplicate keys", () => {
+  expect(parseQueryString("key=&key=")).toEqual({
+    key: ["", ""],
+  });
+});
+
+test("should handle duplicate empty keys", () => {
+  expect(parseQueryString("=one&=two")).toEqual({
+    "": ["one", "two"],
+  });
+});
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..68af13a7a 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,19 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
+
+  const counts = {};
+
+  for (const item of items) {
+    if (counts[item]) {
+      counts[item]++;
+    } else {
+      counts[item] = 1;
+    }
+  }
+
+  return counts;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..b729296c3 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -14,21 +14,81 @@ const tally = require("./tally.js");
  * tally(['a', 'a', 'b', 'c']), target output: { a : 2, b: 1, c: 1 }
  */
 
-// Acceptance criteria:
-
-// Given a function called tally
-// When passed an array of items
-// Then it should return an object containing the count for each unique item
-
 // Given an empty array
 // When passed to tally
 // Then it should return an empty object
-test.todo("tally on an empty array returns an empty object");
+test("tally on an empty array returns an empty object", () => {
+  expect(tally([])).toEqual({});
+});
+
+// Given an array with one item
+// When passed to tally
+// Then it should return the item with a count of 1
+test("tally counts a single item", () => {
+  expect(tally(["a"])).toEqual({
+    a: 1,
+  });
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally counts duplicate items", () => {
+  expect(tally(["a", "a", "a"])).toEqual({
+    a: 3,
+  });
+});
+
+// Given an array with multiple unique items
+// When passed to tally
+// Then it should return the count for each item
+test("tally counts multiple different items", () => {
+  expect(tally(["a", "a", "b", "c"])).toEqual({
+    a: 2,
+    b: 1,
+    c: 1,
+  });
+});
+
+// Given an array with numbers
+// When passed to tally
+// Then it should count numbers correctly
+test("tally counts numbers", () => {
+  expect(tally([1, 1, 2, 3, 3])).toEqual({
+    1: 2,
+    2: 1,
+    3: 2,
+  });
+});
+
+// Given an array with mixed strings
+// When passed to tally
+// Then it should count each string correctly
+test("tally counts different strings", () => {
+  expect(tally(["cat", "dog", "cat", "bird"])).toEqual({
+    cat: 2,
+    dog: 1,
+    bird: 1,
+  });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws an error for invalid input", () => {
+  expect(() => tally("hello")).toThrow();
+});
+
+// Given null as input
+// When passed to tally
+// Then it should throw an error
+test("tally throws an error for null input", () => {
+  expect(() => tally(null)).toThrow();
+});
+
+// Given undefined as input
+// When passed to tally
+// Then it should throw an error
+test("tally throws an error for undefined input", () => {
+  expect(() => tally(undefined)).toThrow();
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..c082c8ef3 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -10,20 +10,22 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
-// a) What is the current return value when invert is called with { a : 1 }
+module.exports = invert;
 
+// a) What is the current return value when invert is called with { a : 1 }
+//{ key: 1 }
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
-
+//{ key: 2 }
 // c) What is the target return value when invert is called with {a : 1, b: 2}
-
+//{ "1": "a", "2": "b" }
 // c) What does Object.entries return? Why is it needed in this program?
-
+//returns an array of key-value pairs and we need both the key and the value to swap them
 // d) Explain why the current return value is different from the target output
-
+//creates a property called "key" instead of using the actual key variable
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..ac0b9632e
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,14 @@
+const invert = require("./invert");
+
+test("inverts an object", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({
+    1: "a",
+    2: "b",
+  });
+});
+
+test("inverts a single key-value pair", () => {
+  expect(invert({ x: 10 })).toEqual({
+    10: "x",
+  });
+});