diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..7ea2ffa88 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,4 +1,6 @@
-// Predict and explain first...
+// The original code used address[0], which doesn't work because
+// address is an object, not an array. Objects have named keys, not numeric indexes.
+// So address[0] is undefined.
 
 // This code should log out the houseNumber from the address object
 // but it isn't working...
@@ -12,4 +14,4 @@ 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..5f2778f0b 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,7 +1,7 @@
-// Predict and explain first...
-
-// 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
+// Prediction and explanation:
+// The original code uses `for (const value of author)`, but `author` is an object,
+// not an array or other iterable. This will throw a TypeError.
+// To fix it, we need to loop over the object's values using Object.values().
 
 const author = {
   firstName: "Zadie",
@@ -11,6 +11,8 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+// Fix: use Object.values() to get an array of the values
+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..478ab5e8c 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,8 +1,8 @@
-// Predict and explain first...
-
-// 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?
+// Prediction and explanation:
+// The current code tries to log the whole `recipe` object with `${recipe}`,
+// but objects are not automatically formatted in a readable way in a template string.
+// This will print something like "[object Object]" instead of the ingredients on separate lines.
+// To fix it, we need to access the `ingredients` array and log each ingredient individually.
 
 const recipe = {
   title: "bruschetta",
@@ -10,6 +10,10 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
+// Fix: log title and serves, then loop over ingredients to print each on a new line
 console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+ingredients:`);
+for (const ingredient of recipe.ingredients) {
+  console.log(ingredient);
+}
+
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..8d7ff5e4a 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,12 @@
-function contains() {}
+function contains(obj, prop) {
+  // Check if the input is a valid object and prop is a string
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    return false;
+  }
+
+  // Use Object.hasOwn to check if property exists
+  return Object.hasOwn(obj, prop);
+}
 
 module.exports = contains;
+
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..5defb9f55 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -1,35 +1,31 @@
 const contains = require("./contains.js");
 
-/*
-Implement a function called contains that checks an object contains a
-particular property
-
-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'
-*/
-
-// 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 object has the property", () => {
+  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 object does not have the property", () => {
+  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
+// Then it should return false
+test("contains returns false for invalid input like arrays", () => {
+  expect(contains([], "a")).toBe(false);
+  expect(contains(null, "a")).toBe(false);
+});
+
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..1b3d6c25a 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,15 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  // Validate input: must be an array of arrays
+  if (!Array.isArray(pairs)) {
+    return {};
+  }
+
+  const lookup = {};
+  for (const [country, currency] of pairs) {
+    lookup[country] = currency;
+  }
+  return lookup;
 }
 
 module.exports = createLookup;
+
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..aea5e7217 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,35 +1,26 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
+test("creates a country currency code lookup for multiple codes", () => {
+  const input = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+  const result = createLookup(input);
+
+  expect(result).toEqual({
+    US: "USD",
+    CA: "CAD",
+    GB: "GBP",
+  });
+});
+
+test("returns empty object when given an empty array", () => {
+  expect(createLookup([])).toEqual({});
+});
+
+test("returns empty object when given invalid input", () => {
+  expect(createLookup(null)).toEqual({});
+  expect(createLookup("not an array")).toEqual({});
+});
 
-/*
-
-Create a lookup object of key value pairs from an array of code pairs
-
-Acceptance Criteria:
-
-Given
- - An array of arrays representing country code and currency code pairs
-   e.g. [['US', 'USD'], ['CA', 'CAD']]
-
-When
- - createLookup function is called with the country-currency array as an argument
-
-Then
- - It should return an object where:
- - The keys are the country codes
- - The values are the corresponding currency codes
-
-Example
-Given: [['US', 'USD'], ['CA', 'CAD']]
-
-When
-createLookup(countryCurrencyPairs) is called
-
-Then
-It should return:
- {
-   'US': 'USD',
-   'CA': 'CAD'
- }
-*/
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..b164b36f5 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -1,16 +1,60 @@
 function parseQueryString(queryString) {
   const queryParams = {};
-  if (queryString.length === 0) {
-    return queryParams;
+
+  // Guard: empty or falsy input
+  if (!queryString) return queryParams;
+
+  // Remove leading '?'
+  if (queryString.startsWith("?")) {
+    queryString = queryString.slice(1);
+    if (queryString.length === 0) return queryParams;
   }
-  const keyValuePairs = queryString.split("&");
 
-  for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+  const pairs = queryString.split("&").filter((p) => p.length > 0);
+
+  const safeDecode = (s) => {
+    // Replace + with space before decoding
+    const replaced = s.replace(/\+/g, " ");
+    try {
+      return decodeURIComponent(replaced);
+    } catch (e) {
+      // If decoding fails, return the replaced string as-is
+      return replaced;
+    }
+  };
+
+  for (const pair of pairs) {
+    const idx = pair.indexOf("=");
+
+    let key;
+    let value;
+    if (idx === -1) {
+      // No '=' present: treat as key with empty string value
+      key = pair;
+      value = "";
+    } else {
+      // Split on first '=' only
+      key = pair.slice(0, idx);
+      value = pair.slice(idx + 1);
+    }
+
+    const decodedKey = safeDecode(key);
+    const decodedValue = safeDecode(value);
+
+    if (Object.prototype.hasOwnProperty.call(queryParams, decodedKey)) {
+      const existing = queryParams[decodedKey];
+      if (Array.isArray(existing)) {
+        existing.push(decodedValue);
+      } else {
+        queryParams[decodedKey] = [existing, decodedValue];
+      }
+    } else {
+      queryParams[decodedKey] = decodedValue;
+    }
   }
 
   return queryParams;
 }
 
 module.exports = parseQueryString;
+
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..62faf1b2d 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -1,12 +1,33 @@
-// In the prep, we implemented a function to parse query strings.
-// Unfortunately, it contains several bugs!
-// Below is one test case for an edge case the implementation doesn't handle well.
-// Fix the implementation for this test, 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("parses querystring values containing =", () => {
   expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+    equation: "x=y+1",
   });
 });
+
+test("parses basic key/value pairs", () => {
+  expect(parseQueryString("a=1&b=2")).toEqual({ a: "1", b: "2" });
+});
+
+test("handles empty query string", () => {
+  expect(parseQueryString("")).toEqual({});
+  expect(parseQueryString("?")).toEqual({});
+});
+
+test("handles keys without value and keys with empty value", () => {
+  expect(parseQueryString("noValue")).toEqual({ noValue: "" });
+  expect(parseQueryString("empty=")).toEqual({ empty: "" });
+});
+
+test("decodes percent-encoding and plus signs", () => {
+  expect(parseQueryString("name=John%20Doe&query=hello+world")).toEqual({
+    name: "John Doe",
+    query: "hello world",
+  });
+});
+
+test("collects duplicate keys into arrays in order", () => {
+  expect(parseQueryString("a=1&a=2&a=3")).toEqual({ a: ["1", "2", "3"] });
+});
+
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..0e7c78c49 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,18 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("Input must be an array");
+  }
+
+const result = Object.create(null);
+  for (const item of items) {
+    if (result[item]) {
+      result[item] ++;
+    } else {
+      result[item] = 1;
+    }
+  }
+  return result;
+}
 
 module.exports = tally;
+
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..1acb0ef2b 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -1,34 +1,27 @@
 const tally = require("./tally.js");
 
-/**
- * tally array
- *
- * In this task, you'll need to implement a function called tally
- * that will take a list of items and count the frequency of each item
- * in an array
- *
- * For example:
- *
- * tally(['a']), target output: { a: 1 }
- * tally(['a', 'a', 'a']), target output: { a: 3 }
- * 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 duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally counts items correctly", () => {
+  expect(tally(["a"])).toEqual({ a: 1 });
+  expect(tally(["a", "a", "a"])).toEqual({ a: 3 });
+  expect(tally(["a", "a", "b", "c"])).toEqual({ a: 2, b: 1, c: 1 });
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally throws error for invalid input", () => {
+  expect(() => tally("not an array")).toThrow("Input must be an array");
+  expect(() => tally(null)).toThrow("Input must be an array");
+  expect(() => tally(123)).toThrow("Input must be an array");
+});
+
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..d38c98b3b 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -1,5 +1,3 @@
-// Let's define how invert should work
-
 // Given an object
 // When invert is passed this object
 // Then it should swap the keys and values in the object
@@ -10,20 +8,32 @@ function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key; // fix: use computed property instead of "key"
   }
 
   return invertedObj;
 }
 
+module.exports = invert;
+
 // a) What is the current return value when invert is called with { a : 1 }
+// Answer: { key: 1 }
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// Answer: { key: 2 } (the second assignment overwrites the first)
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// Answer: { "1": "a", "2": "b" }
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Answer: Object.entries(obj) returns an array of [key, value] pairs.
+// Example: Object.entries({a:1, b:2}) → [["a",1],["b",2]].
+// It’s needed because for...of can iterate over these pairs easily.
 
 // d) Explain why the current return value is different from the target output
+// Answer: The code used invertedObj.key = value, which creates a property literally
+// called "key". We need invertedObj[value] = key to swap properly.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// Answer: Fixed above by changing to invertedObj[value] = key.
+
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..e4aaaa675
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,20 @@
+const invert = require("./invert.js");
+
+test("inverts a single key-value pair", () => {
+  expect(invert({ a: 1 })).toEqual({ 1: "a" });
+});
+
+test("inverts multiple key-value pairs", () => {
+  expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+});
+
+test("works with string values", () => {
+  expect(invert({ x: "hello", y: "world" })).toEqual({
+    hello: "x",
+    world: "y",
+  });
+});
+
+test("returns empty object when input is empty", () => {
+  expect(invert({})).toEqual({});
+});
diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..9e3816fe2 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -1,28 +1,70 @@
-/*
-  Count the number of times a word appears in a given string.
+// Basic implementation of word counting
+
+
+// Given a string of words
+// When the string is passed to countWords
+// Then it should return an object with the count of each word
+
+// Example:
+// Given "you and me and you"
+// When countWords is called on this string
+// Then it should return { you: 2, and: 2, me: 1 }
 
-  Write a function called countWords that
-    - takes a string as an argument
-    - returns an object where
-          - the keys are the words from the string and
-          - the values are the number of times the word appears in the string
+function countWords(str) {
+  const counts = {};
 
-  Example
-  If we call countWords like this:
+  // ✅ Basic: split on spaces
+  const words = str.split(" ");
 
-  countWords("you and me and you") then the target output is { you: 2, and: 2, me: 1 }
+  for (const word of words) {
+    if (!counts[word]) {
+      counts[word] = 1;
+    } else {
+      counts[word]++;
+    }
+  }
 
-  To complete this exercise you should understand
-    - Strings and string manipulation
-    - Loops
-    - Comparison inside if statements
-    - Setting values on an object
+  return counts;
+}
+
+module.exports = countWords;
+
+
+// Advanced challenges are implemented in countWordsAdvanced
+/*
+### Advanced challenges (implemented separately)
 
-## Advanced challenges
+1. Remove punctuation
+   → Use regex to strip punctuation before splitting.
 
-1. Remove all of the punctuation (e.g. ".", ",", "!", "?") to tidy up the results
+2. Ignore case
+   → Convert the string to lowercase before counting.
 
-2. Ignore the case of the words to find more unique words. e.g. (A === a, Hello === hello)
+3. Order results
+   → Convert the counts object into an array, sort it, and return it in order.
 
-3. Order the results to find out which word is the most common in the input
 */
+
+function countWordsAdvanced(str) {
+  const counts = Object.create(null);
+
+  // 1. Remove punctuation
+  const noPunctuation = str.replace(/[.,!?]/g, "");
+
+  // 2. Ignore case
+  const words = noPunctuation.toLowerCase().split(/\s+/);
+
+  for (const word of words) {
+    if (!word) continue; // skip empty strings
+    counts[word] = (counts[word] || 0) + 1;
+  }
+
+  // 3. Order results (most common first)
+  const sortedEntries = Object.entries(counts).sort((a, b) => b[1] - a[1]);
+
+  return Object.fromEntries(sortedEntries);
+}
+
+// Example usage
+// console.log(countWords("you and me and you"));
+// console.log(countWordsAdvanced("You, you! and me? And YOU."));
\ No newline at end of file
diff --git a/Sprint-2/stretch/mode.js b/Sprint-2/stretch/mode.js
index 3f7609d79..b16a42a95 100644
--- a/Sprint-2/stretch/mode.js
+++ b/Sprint-2/stretch/mode.js
@@ -1,28 +1,22 @@
-// You are given an implementation of calculateMode
-
-// calculateMode's implementation can be broken down into two stages:
-
-// Stage 1. One part of the code tracks the frequency of each value
-// Stage 2. The other part finds the value with the highest frequency
-
-// refactor calculateMode by splitting up the code
-// into smaller functions using the stages above
-
-function calculateMode(list) {
-  // track frequency of each value
+// Stage 1. Track frequency of each value
+function buildFrequencyMap(list) {
   let freqs = new Map();
 
   for (let num of list) {
     if (typeof num !== "number") {
-      continue;
+      continue; // skip non-number values
     }
-
     freqs.set(num, (freqs.get(num) || 0) + 1);
   }
 
-  // Find the value with the highest frequency
+  return freqs;
+}
+
+// Stage 2. Find the value with the highest frequency
+function findMode(freqs) {
   let maxFreq = 0;
   let mode;
+
   for (let [num, freq] of freqs) {
     if (freq > maxFreq) {
       mode = num;
@@ -33,4 +27,11 @@ function calculateMode(list) {
   return maxFreq === 0 ? NaN : mode;
 }
 
+// Main function
+function calculateMode(list) {
+  const freqs = buildFrequencyMap(list);
+  return findMode(freqs);
+}
+
 module.exports = calculateMode;
+
diff --git a/Sprint-2/stretch/till.js b/Sprint-2/stretch/till.js
index 6a08532e7..1b051be9b 100644
--- a/Sprint-2/stretch/till.js
+++ b/Sprint-2/stretch/till.js
@@ -8,12 +8,17 @@ function totalTill(till) {
   let total = 0;
 
   for (const [coin, quantity] of Object.entries(till)) {
-    total += coin * quantity;
+    // coin is a string like "1p", "20p"
+    // We need to strip the "p" and convert it into a number of pennies
+    const coinValue = parseInt(coin, 10);
+    total += coinValue * quantity;
   }
 
-  return `£${total / 100}`;
+  return `£${(total / 100).toFixed(2)}`;
 }
 
+module.exports = totalTill;
+
 const till = {
   "1p": 10,
   "5p": 6,
@@ -23,9 +28,17 @@ const till = {
 const totalAmount = totalTill(till);
 
 // a) What is the target output when totalTill is called with the till object
+// Answer: £3.60 (10x1p + 6x5p + 4x50p + 10x20p = 360p = £3.60)
 
 // b) Why do we need to use Object.entries inside the for...of loop in this function?
+// Answer: Object.entries(till) returns an array of [coin, quantity] pairs,
+// allowing us to iterate over both the coin name (e.g. "50p") and its count.
 
 // c) What does coin * quantity evaluate to inside the for...of loop?
+// Answer (before fix): NaN, because coin is a string like "50p". 
+// After fix: coinValue * quantity gives the total pennies for that coin type.
 
 // d) Write a test for this function to check it works and then fix the implementation of totalTill
+// Answer: Fix shown above to parse coin values correctly.
+
+
diff --git a/Sprint-2/stretch/till.test.js b/Sprint-2/stretch/till.test.js
new file mode 100644
index 000000000..255a0db88
--- /dev/null
+++ b/Sprint-2/stretch/till.test.js
@@ -0,0 +1,14 @@
+// Example test (till.test.js):
+   
+const totalTill = require("./till.js");
+
+describe("totalTill()", () => {
+  test("calculates the total amount in pounds", () => {
+    const till = { "1p": 10, "5p": 6, "50p": 4, "20p": 10 };
+    expect(totalTill(till)).toBe("£3.60");
+  });
+
+  test("returns £0.00 for an empty till", () => {
+    expect(totalTill({})).toBe("£0.00");
+  });
+});