diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..d9fc08b5a 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -12,4 +12,6 @@ const address = {
   postcode: "XYZ 123",
 };
 
-console.log(`My house number is ${address[0]}`);
+console.log(`My house number is ${address.houseNumber}`);
+
+//address is an object without a key, therefore address[0] is undefined. To fix this we write "address.houseNumber".
\ No newline at end of file
diff --git a/Sprint-2/debug/author.js b/Sprint-2/debug/author.js
index 8c2125977..3df469f06 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -11,6 +11,7 @@ const author = {
   alive: true,
 };
 
-for (const value of author) {
+for (const value in author) {
   console.log(value);
 }
+// for...of works only with iterable objects like arrays, strings, maps..etc. In order to fix this problem we can use "for...in" to loop through the keys of the object.
\ No newline at end of file
diff --git a/Sprint-2/debug/recipe.js b/Sprint-2/debug/recipe.js
index 6cbdd22cd..76714b2c7 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -10,6 +10,9 @@ const recipe = {
   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
 };
 
-console.log(`${recipe.title} serves ${recipe.serves}
-  ingredients:
-${recipe}`);
+
+console.log(`${recipe.title} serves ${recipe.serves} ingredients:`);
+for(let ingredient of recipe.ingredients) {
+  console.log(ingredient)
+}
+//I used a for...of loop to list each ingredient on a new line.
\ No newline at end of file
diff --git a/Sprint-2/implement/contains.js b/Sprint-2/implement/contains.js
index cd779308a..d3c9971df 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,8 @@
-function contains() {}
+function contains(obj, propName) {
+    if (typeof obj !== "object" || obj === null || Array.isArray(obj)) {
+        return false;
+    }
+    return propName in obj;
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..204564de4 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -16,20 +16,39 @@ as the object doesn't contains a key of 'c'
 // 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
+describe("contains", () => {
+    test("returns true if the object contains the property, false otherwise", () => {
+        expect(contains({CYF:3,ITP:5}, "ITP")).toBe(true);
+    })
 
 // 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("returns true for an existing property", () => {
+    expect(contains({ a: 1, b: 2 }, "a")).toBe(true);
+    expect(contains({ x: 10, y: 20 }, "y")).toBe(true);
+  });
 // Given an object with properties
 // When passed to contains with a non-existent property name
 // Then it should return false
+  test("returns false for a non-existent property", () => {
+    expect(contains({ a: 1, b: 2 }, "c")).toBe(false);
+    expect(contains({ x: 10, y: 20 }, "z")).toBe(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 parameters like an array", () => {
+    expect(contains([], "a")).toBe(false);
+    expect(contains(null, "a")).toBe(false);
+    expect(contains("string", "a")).toBe(false);
+  });
+});
\ No newline at end of file
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..3ed07e988 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,9 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  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..a0f6e17e2 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 input = [['US', 'USD'], ['CA', 'CAD'], ['JP', 'JPY']];
+    const expected = {
+      US: 'USD',
+      CA: 'CAD',
+      JP: 'JPY'
+    };
+
+    expect(createLookup(input)).toEqual(expected);
+  });
+
 
 /*
 
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..84b6a41fa 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -6,7 +6,9 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
+    const index = pair.indexOf("=");
+    const key = pair.slice(0, index);
+    const value = pair.slice(index + 1);
     queryParams[key] = value;
   }
 
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 3e218b789..7dae339b2 100644
--- a/Sprint-2/implement/querystring.test.js
+++ b/Sprint-2/implement/querystring.test.js
@@ -5,8 +5,22 @@
 
 const parseQueryString = require("./querystring.js")
 
-test("parses querystring values containing =", () => {
-  expect(parseQueryString("equation=x=y+1")).toEqual({
-    "equation": "x=y+1",
+describe("querystring parser", () => {
+  test("parses querystring values containing =", () => {
+    expect(parseQueryString("equation=x=y+1")).toEqual({
+      "equation": "x=y+1",
+    });
   });
-});
+  test("returns empty object for empty query string", () => {
+    expect(parseQueryString("")).toEqual({});
+  });
+  test("handles key with missing value", () => {
+    expect(parseQueryString("key=")).toEqual({ key: "" });
+  });
+  test("handles missing key with value", () => {
+    expect(parseQueryString("=value")).toEqual({ "": "value" });
+  });
+  test("handles multiple key-value pairs", () => {
+    expect(parseQueryString("a=1&b=2")).toEqual({ a: "1", b: "2" });
+  });
+  })
\ No newline at end of file
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..c3192d498 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,17 @@
-function tally() {}
+function tally(arr) {
+    if (!Array.isArray(arr)) {
+    throw new Error("Input must be an array");
+  }
+
+  const result = {};
+  for (const item of arr) {
+    if (result[item] === undefined) {
+      result[item] = 1;
+    } 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..19267fa3f 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -19,16 +19,28 @@ const tally = require("./tally.js");
 // Given a function called tally
 // When passed an array of items
 // Then it should return an object containing the count for each unique item
-
+describe("tally test", () => {
+test("tally counts each unique item correctly", () => {
+  expect(tally(["a", "b", "c"])).toEqual({ a: 1, b: 1, c: 1 });
+});
 // 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 correctly", () => {
+  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 an error for invalid input", () => {
+  expect(() => tally("CYF")).toThrow("Input must be an array");
+});
+});
\ No newline at end of file
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..2f5f84497 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -10,20 +10,34 @@ 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 }
-
+//{ 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?
-
+// Object.entries gives an array of [key, value] pairs.
 // d) Explain why the current return value is different from the target output
-
+// invertedObj.key sets a property literally called "key". We need to use the variable key as the dynamic property name. and we need to change "key" to "value" and "value" to "key".
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+console.assert(
+  JSON.stringify(invert({ a: 1, b: 2 })) === JSON.stringify({ "1": "a", "2": "b" }),
+  "multiple keys test failed"
+);
+console.assert(
+  JSON.stringify(invert({ x: "hello", y: "world" })) === JSON.stringify({ "hello": "x", "world": "y" }),
+  "string cases test failed"
+);
+console.assert(
+  JSON.stringify(invert({})) === JSON.stringify({}),
+  "empty test failed"
+);
+console.log("All tests passed!");