diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..ff917efcf 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -1,5 +1,11 @@
 // Predict and explain first...
 
+// This will log "My house number is undefined" because
+// address[0] is looking for index 0 like it's an array, but address
+// is an object. To get a value from an object you need to use the
+// key name, not a number. Changing address[0] to address.houseNumber
+// will fix it and log "My house number is 42".
+
 // This code should log out the houseNumber from the address object
 // but it isn't working...
 // Fix anything that isn't working
@@ -12,4 +18,4 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
\ No newline at end of file
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..1f17654e4 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -1,4 +1,6 @@
 // Predict and explain first...
+// This code will throw a TypeError: "author is not iterable".
+//
 
 // 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 +13,6 @@ 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..133b10bd1 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -1,9 +1,14 @@
 // Predict and explain first...
+// This will not log the ingredients correctly. It will print the whole
+// recipe object as [object Object] instead of each ingredient on its own line,
+// because you're interpolating the entire object (`${recipe}`) instead of
+// its properties and the ingredients array items.
 
 // 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?
 
+
 const recipe = {
   title: "bruschetta",
   serves: 2,
@@ -11,5 +16,8 @@ const recipe = {
 };
 
 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..5104e0abc 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,11 @@
-function contains() {}
+function contains(obj, propName) {
+  // Return false for non-objects or null
+  if (obj === null || typeof obj !== "object" || Array.isArray(obj)) {
+    return false;
+  }
+
+  // Check if the object has the property as its own key
+  return Object.hasOwn(obj, propName);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..0309083ae 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -1,35 +1,55 @@
 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 for existing 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 for non-existent 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
+test("contains with invalid parameters returns false", () => {
+  expect(contains([], "a")).toBe(false);
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..45c28dc96 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,12 @@
-function createLookup() {
+function createLookup(countryCurrencyPairs) {
   // implementation here
+  const lookup = {};
+
+  for (const [countryCode, currencyCode] of countryCurrencyPairs) {
+    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..0b404334a 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,31 +1,54 @@
 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 countryCurrencyPairs = [
+    ["US", "USD"],
+    ["CA", "CAD"],
+    ["GB", "GBP"],
+  ];
+
+  const result = createLookup(countryCurrencyPairs);
+
+  expect(result).toEqual({
+    US: "USD",
+    CA: "CAD",
+    GB: "GBP",
+  });
+});
+
 
 /*
 
+
 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:
  {
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..1d3ea920d 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -3,14 +3,32 @@ function parseQueryString(queryString) {
   if (queryString.length === 0) {
     return queryParams;
   }
+
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    if (pair === "") {
+      continue;
+    }
+
+    const indexOfEquals = pair.indexOf("=");
+    let key;
+    let value;
+
+    if (indexOfEquals === -1) {
+      // no "=", treat whole pair as key with empty value
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, indexOfEquals);
+      value = pair.slice(indexOfEquals + 1);
+    }
+
     queryParams[key] = value;
   }
 
   return queryParams;
 }
 
+
 module.exports = parseQueryString;
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..a1ca896fb 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -3,10 +3,34 @@
 // 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")
 
+
 test("parses querystring values containing =", () => {
   expect(parseQueryString("equation=x=y+1")).toEqual({
     "equation": "x=y+1",
   });
 });
+
+test("parses empty querystring as empty object", () => {
+  expect(parseQueryString("")).toEqual({});
+});
+
+test("parses single key with empty value", () => {
+  expect(parseQueryString("flag=")).toEqual({ flag: "" });
+});
+
+test("parses key with no =", () => {
+  expect(parseQueryString("flag")).toEqual({ flag: "" });
+});
+
+test("parses multiple key value pairs", () => {
+  expect(parseQueryString("a=1&b=2")).toEqual({ a: "1", b: "2" });
+});
+
+test("later duplicate keys overwrite earlier ones", () => {
+  expect(parseQueryString("a=1&a=2")).toEqual({ a: "2" });
+});
+
+
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..c666a88d6 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,15 @@
-function tally() {}
+function tally(items) {
+  if (!Array.isArray(items)) {
+    throw new Error("tally expects an array");
+  }
 
-module.exports = tally;
+  const counts = {};
+
+  for (const item of items) {
+    counts[item] = (counts[item] || 0) + 1;
+  }
+
+  return counts;
+}
+
+module.exports = tally;
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..00be55545 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -1,5 +1,6 @@
 const tally = require("./tally.js");
 
+
 /**
  * tally array
  *
@@ -14,21 +15,39 @@ 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 duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally counts each unique item", () => {
+  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 on invalid input", () => {
+  expect(() => tally("not an array")).toThrow();
+});
+
+
+
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..81f7ad271 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -1,29 +1,49 @@
 // 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
 
+
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
+
 function invert(obj) {
   const invertedObj = {};
 
   for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
+    invertedObj[value] = key;
   }
 
   return invertedObj;
 }
 
+module.exports = invert;
+
+
 // a) What is the current return value when invert is called with { a : 1 }
+// Answer: { "1": "a" }
+
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// Answer: { "1": "a", "2": "b" }
+
 
 // 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,
+// It is needed so we can loop over the object and easily get both key and value in the for...of loop using array destructuring: [key, value].
+
 
 // d) Explain why the current return value is different from the target output
+// Answer: In this implementation, the current return value already matches the target output, because we correctly use the value as the new key
+// and the key as the new value: invertedObj[value] = key.
+
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+// Answer: No changes needed to the implementation; it already works as required.
+
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..e705e65af
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,17 @@
+const invert = require("./invert.js");
+
+// Given an object
+// When invert is passed this object
+// Then it should swap the keys and values in the object
+
+test("inverts 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("inverts empty object to empty object", () => {
+  expect(invert({})).toEqual({});
+});
diff --git a/Sprint-2/stretch/count-words.js b/Sprint-2/stretch/count-words.js
index 8e85d19d7..25bbd3e84 100644
--- a/Sprint-2/stretch/count-words.js
+++ b/Sprint-2/stretch/count-words.js
@@ -1,28 +1,55 @@
 /*
   Count the number of times a word appears in a given string.
 
+
   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
 
+
   Example
   If we call countWords like this:
 
+
   countWords("you and me and you") then the target output is { you: 2, and: 2, me: 1 }
 
+
   To complete this exercise you should understand
     - Strings and string manipulation
     - Loops
     - Comparison inside if statements
     - Setting values on an object
 
+
 ## Advanced challenges
 
+
 1. Remove all of the punctuation (e.g. ".", ",", "!", "?") to tidy up the results
 
+
 2. Ignore the case of the words to find more unique words. e.g. (A === a, Hello === hello)
 
+
 3. Order the results to find out which word is the most common in the input
 */
+
+
+
+function countWords(str) {
+  const counts = {};
+
+  const words = str.split(" ").filter((w) => w !== "");
+
+  for (const word of words) {
+    if (counts[word]) {
+      counts[word] += 1;
+    } else {
+      counts[word] = 1;
+    }
+  }
+
+  return counts;
+}
+
diff --git a/Sprint-2/stretch/mode.js b/Sprint-2/stretch/mode.js
index 3f7609d79..988355538 100644
--- a/Sprint-2/stretch/mode.js
+++ b/Sprint-2/stretch/mode.js
@@ -1,18 +1,21 @@
 // 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
-  let freqs = new Map();
 
-  for (let num of list) {
+function getFrequencies(list) {
+  const freqs = new Map();
+
+  for (const num of list) {
     if (typeof num !== "number") {
       continue;
     }
@@ -20,10 +23,14 @@ function calculateMode(list) {
     freqs.set(num, (freqs.get(num) || 0) + 1);
   }
 
-  // Find the value with the highest frequency
+  return freqs;
+}
+
+function getModeFromFrequencies(freqs) {
   let maxFreq = 0;
   let mode;
-  for (let [num, freq] of freqs) {
+
+  for (const [num, freq] of freqs) {
     if (freq > maxFreq) {
       mode = num;
       maxFreq = freq;
@@ -33,4 +40,9 @@ function calculateMode(list) {
   return maxFreq === 0 ? NaN : mode;
 }
 
+function calculateMode(list) {
+  const freqs = getFrequencies(list);
+  return getModeFromFrequencies(freqs);
+}
+
 module.exports = calculateMode;
diff --git a/Sprint-2/stretch/mode.test.js b/Sprint-2/stretch/mode.test.js
index ca33c28a3..dba406876 100644
--- a/Sprint-2/stretch/mode.test.js
+++ b/Sprint-2/stretch/mode.test.js
@@ -1,16 +1,20 @@
 const calculateMode = require("./mode.js");
 
+
 // Acceptance criteria for calculateMode function
 
+
 // Given an array of numbers
 // When calculateMode is called on the array
 // Then it should return the number that appears most frequently in the array
 
+
 // Example:
 // Given [2,4,1,2,3,2,1]
 // When calculateMode is called on [2,4,1,2,3,2,1]
 // Then it should return 2 */
 
+
 describe("calculateMode()", () => {
   test("returns the most frequent number in an array", () => {
     const nums = [2, 4, 1, 2, 3, 2, 1];
diff --git a/Sprint-2/stretch/till.js b/Sprint-2/stretch/till.js
index 6a08532e7..10e5d73c5 100644
--- a/Sprint-2/stretch/till.js
+++ b/Sprint-2/stretch/till.js
@@ -1,19 +1,23 @@
 // totalTill takes an object representing coins in a till
 
+
 // Given an object of coins
 // When this till object is passed to totalTill
 // Then it should return the total amount in pounds
 
+
 function totalTill(till) {
   let total = 0;
 
   for (const [coin, quantity] of Object.entries(till)) {
-    total += coin * quantity;
+    const valueInPence = Number(coin.replace("p", ""));
+    total += valueInPence * quantity;
   }
 
   return `£${total / 100}`;
 }
 
+
 const till = {
   "1p": 10,
   "5p": 6,
@@ -22,10 +26,17 @@ const till = {
 };
 const totalAmount = totalTill(till);
 
+
 // a) What is the target output when totalTill is called with the till object
+// "£4.4"
+
 
 // b) Why do we need to use Object.entries inside the for...of loop in this function?
+// Object.entries returns [coin, quantity] pairs, allowing destructuring in the loop
+
 
 // c) What does coin * quantity evaluate to inside the for...of loop?
+// Original: "1p" * 10 = NaN. Fixed: 1 * 10 = 10 (pence for that coin type)
+
 
-// d) Write a test for this function to check it works and then fix the implementation of totalTill
+module.exports = totalTill;
diff --git a/Sprint-2/stretch/totalTill.test.js b/Sprint-2/stretch/totalTill.test.js
new file mode 100644
index 000000000..bf1fc563a
--- /dev/null
+++ b/Sprint-2/stretch/totalTill.test.js
@@ -0,0 +1,6 @@
+const totalTill = require("./totalTill.js");
+
+test("calculates total till value in pounds", () => {
+  const till = { "1p": 10, "5p": 6, "50p": 4, "20p": 10 };
+  expect(totalTill(till)).toBe("£4.4");
+});