diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..f28985431 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -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}`);
\ No newline at end of file
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..7ba8f4c75 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -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..a413b3332 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -12,4 +12,4 @@ const recipe = {
 
 console.log(`${recipe.title} serves ${recipe.serves}
   ingredients:
-${recipe}`);
+${recipe.ingredients.join("\n")}`);
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..2e8290e79 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,9 @@
-function contains() {}
+function contains(obj, key) {
+  if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+    return false;
+  }
 
-module.exports = contains;
+  return Object.keys(obj).includes(key);
+}
+
+module.exports = contains;
\ No newline at end of file
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..90c3309d9 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -20,16 +20,28 @@ as the object doesn't contains a key of 'c'
 // 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")).toEqual(false);
+});
 
 // Given an object with properties
 // When passed to contains with an existing property name
 // Then it should return true
+test("returns true when object has the property", () => {
+  expect(contains({ a: 1, b: 2 }, "a")).toEqual(true);
+});
 
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+test("returns false when object doesn't have the property", () => {
+  expect(contains({ a: 1, b: 2 }, "c")).toEqual(false);
+});
 
 // Given invalid parameters like an array
 // When passed to contains
 // Then it should return false or throw an error
+test("returns false for invalid input like an array", () => {
+  expect(contains([1, 2, 3], "a")).toEqual(false);
+});
+
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..da5b177d4 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,11 @@
-function createLookup() {
-  // implementation here
+function createLookup(countryCurrencyPairs) {
+  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..b3bd1c68d 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,6 +1,16 @@
 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"],
+  ];
+
+  expect(createLookup(countryCurrencyPairs)).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});
 
 /*
 
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..ce1c88733 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -6,7 +6,24 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    if (pair === "") {
+      continue;
+    }
+
+    const separatorIndex = pair.indexOf("=");
+    let key;
+    let value;
+
+    if (separatorIndex === -1) {
+      key = pair;
+      value = "";
+    } else {
+      key = pair.slice(0, separatorIndex);
+      value = pair.slice(separatorIndex + 1);
+    }
+
+    key = decodeURIComponent(key.replace(/\+/g, " "));
+    value = decodeURIComponent(value.replace(/\+/g, " "));
     queryParams[key] = value;
   }
 
@@ -14,3 +31,4 @@ function parseQueryString(queryString) {
 }
 
 module.exports = parseQueryString;
+
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..fe30a222e 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -37,12 +37,3 @@ test("should replace '+' by ' '", () => {
   });
 });
 
-// Stretch exercise: Handling query strings that contain identical keys
-
-// Delete this test if you are not working on this optional case
-test("should store values of a key in an array when the key has 2 or more values", () => {
-  expect(parseQueryString("key=value1&key=value2&key=value3&foo=bar")).toEqual({
-    key: ["value1", "value2", "value3"],
-    foo: "bar",
-  });
-});
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..6f309a567 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,15 @@
-function tally() {}
+function tally(items) {
+  if (typeof items === "string" || !Array.isArray(items)) {
+    throw new Error("tally expects an array");
+  }
+
+  const counts = {};
+
+  for (const item of items) {
+    counts[item] = (counts[item] || 0) + 1;
+  }
+
+  return counts;
+}
 
 module.exports = tally;
diff --git a/Sprint-2/implement/tally.test.js b/Sprint-2/implement/tally.test.js
index 2ceffa8dd..86e7c1333 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -23,8 +23,9 @@ const tally = require("./tally.js");
 // 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
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..a077cc071 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -10,20 +10,40 @@ 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 }
+// Answer: { key: 1 } — the loop runs once, and the old buggy line
+// invertedObj.key = value set a literal property called "key" to 1.
 
 // b) What is the current return value when invert is called with { a: 1, b: 2 }
+// Answer: { key: 2 } — the loop runs twice, and each time it overwrote the
+// same literal "key" property, so only the last value (2) survived.
 
 // c) What is the target return value when invert is called with {a : 1, b: 2}
+// Answer: { 1: "a", 2: "b" } — each original value becomes a key, and each
+// original key becomes the value at that new key.
 
 // c) What does Object.entries return? Why is it needed in this program?
+// Answer: Object.entries(obj) returns an array of [key, value] pairs for
+// every property in obj, e.g. Object.entries({a: 1, b: 2}) returns
+// [["a", 1], ["b", 2]]. It's needed because inverting requires both the
+// key and value together at the same time, so each can be swapped into
+// the other's position.
 
 // d) Explain why the current return value is different from the target output
+// Answer: the original code used invertedObj.key = value, where .key is
+// a literal property name (the string "key"), not the loop variable key.
+// So every iteration overwrote the same fixed property instead of creating
+// a new one, and it also assigned in the wrong direction (value into a key
+// slot named "key", instead of swapping key and value with each other).
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+console.log(invert({ x: 10, y: 20 })); // should print { '10': 'x', '20': 'y' }
+console.log(invert({ a: 1, b: 2 })); // should print { '1': 'a', '2': 'b' }
+
+module.exports = invert;