diff --git a/Sprint-2/debug/address.js b/Sprint-2/debug/address.js
index 940a6af83..c8d86db83 100644
--- a/Sprint-2/debug/address.js
+++ b/Sprint-2/debug/address.js
@@ -4,6 +4,20 @@
 // but it isn't working...
 // Fix anything that isn't working
 
+// const address = {
+//   houseNumber: 42,
+//   street: "Imaginary Road",
+//   city: "Manchester",
+//   country: "England",
+//   postcode: "XYZ 123",
+// };
+//
+// console.log(`My house number is ${address[0]}`);
+
+// => in line 15, the object is being called, but the index, instead of a key
+// is put inside the square brackets. This should result in undefined value, since
+// we are treating object as an array.
+
 const address = {
   houseNumber: 42,
   street: "Imaginary Road",
@@ -12,4 +26,4 @@ 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..8d57e8e46 100644
--- a/Sprint-2/debug/author.js
+++ b/Sprint-2/debug/author.js
@@ -3,6 +3,24 @@
 // 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
 
+// const author = {
+//   firstName: "Zadie",
+//   lastName: "Smith",
+//   occupation: "writer",
+//   age: 40,
+//   alive: true,
+// };
+//
+// for (const value of author) {
+//   console.log(value);
+// }
+
+// The script will result in an error because we are trying to loop through the elements
+// of the object, more precisely, through the values of the key-value pairs.
+// The solution written like this would work if author would have been an array.
+// For an object, we need to do an extra specification of the data we want to,b,
+// loop through.
+
 const author = {
   firstName: "Zadie",
   lastName: "Smith",
@@ -11,6 +29,6 @@ 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..cea0615ee 100644
--- a/Sprint-2/debug/recipe.js
+++ b/Sprint-2/debug/recipe.js
@@ -4,6 +4,19 @@
 // Each ingredient should be logged on a new line
 // How can you fix it?
 
+// const recipe = {
+//   title: "bruschetta",
+//   serves: 2,
+//   ingredients: ["olive oil", "tomatoes", "salt", "pepper"],
+// };
+//
+// console.log(`${recipe.title} serves ${recipe.serves}
+//   ingredients:
+// ${recipe}`);
+
+// there's an error in line 15. Instead of logging all the ingredients, line by line, the code is telling to give the whole object
+// and the representation of it will be logged into the console.
+
 const recipe = {
   title: "bruschetta",
   serves: 2,
@@ -11,5 +24,8 @@ 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..834b1b6f2 100644
--- a/Sprint-2/implement/contains.js
+++ b/Sprint-2/implement/contains.js
@@ -1,3 +1,8 @@
-function contains() {}
+function contains(obj, searchKey) {
+  if (Array.isArray(obj)) {
+    throw new Error("Invalid parameters");
+  }
+  return Object.keys(obj).includes(searchKey);
+}
 
 module.exports = contains;
diff --git a/Sprint-2/implement/contains.test.js b/Sprint-2/implement/contains.test.js
index 326bdb1f2..0147ab9f3 100644
--- a/Sprint-2/implement/contains.test.js
+++ b/Sprint-2/implement/contains.test.js
@@ -12,24 +12,39 @@ 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");
-
-// Given an object with properties
-// When passed to contains with an existing property name
-// Then it should return true
-
-// Given an object with properties
-// When passed to contains with a non-existent property name
-// Then it should return false
-
-// Given invalid parameters like an array
-// When passed to contains
-// Then it should return false or throw an error
+describe("contains function", () => {
+  // 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
+  it("given an object and a property name, returns true if the object contains the property, false otherwise", () => {
+    expect(contains({ first: 1, second: 2 }, "first")).toEqual(true);
+    expect(contains({ first: 1, second: 2 }, "third")).toEqual(false);
+  });
+  // Given an empty object
+  // When passed to contains
+  // Then it should return false
+  it("contains on empty object returns false", () => {
+    expect(contains({}, "a")).toBeFalsy();
+  });
+
+  // Given an object with properties
+  // When passed to contains with an existing property name
+  // Then it should return true
+
+  it("given an object and a property name, returns true if the object contains the property", () => {
+    expect(contains({ a: 1, b: 2 }, "a")).toBeTruthy();
+  });
+  // Given an object with properties
+  // When passed to contains with a non-existent property name
+  // Then it should return false
+  it("given an object and a property name, returns false if the object does not contain the property", () => {
+    expect(contains({ a: 1, b: 2 }, "c")).toBeFalsy();
+  });
+  // Given invalid parameters like an array
+  // When passed to contains
+  // Then it should return false or throw an error
+  it("given and invalid parameters, returns false or throws an error", () => {
+    expect(() => contains([1, 2, 3], 3)).toThrow("Invalid parameters");
+    expect(contains({ a: 100, b: 200 }, [100, 200])).toBeFalsy();
+  });
+});
diff --git a/Sprint-2/implement/lookup.js b/Sprint-2/implement/lookup.js
index a6746e07f..f06854541 100644
--- a/Sprint-2/implement/lookup.js
+++ b/Sprint-2/implement/lookup.js
@@ -1,5 +1,10 @@
-function createLookup() {
-  // implementation here
+function createLookup(pairs) {
+  const countryCurrencyObj = {};
+
+  pairs.forEach(([countryCode, currencyCode]) => {
+    countryCurrencyObj[countryCode] = currencyCode;
+  });
+  return countryCurrencyObj;
 }
 
 module.exports = createLookup;
diff --git a/Sprint-2/implement/lookup.test.js b/Sprint-2/implement/lookup.test.js
index 547e06c5a..09f969c25 100644
--- a/Sprint-2/implement/lookup.test.js
+++ b/Sprint-2/implement/lookup.test.js
@@ -1,7 +1,5 @@
 const createLookup = require("./lookup.js");
 
-test.todo("creates a country currency code lookup for multiple codes");
-
 /*
 
 Create a lookup object of key value pairs from an array of code pairs
@@ -33,3 +31,25 @@ It should return:
    'CA': 'CAD'
  }
 */
+
+test("creates a country currency code lookup for single code pair", () => {
+  expect(createLookup([["US", "USD"]])).toEqual({
+    US: "USD",
+  });
+
+  expect(createLookup([["CA", "CAD"]])).toEqual({
+    CA: "CAD",
+  });
+});
+
+test("creates a country currency code lookup for multiple codes", () => {
+  expect(
+    createLookup([
+      ["US", "USD"],
+      ["CA", "CAD"],
+    ])
+  ).toEqual({
+    US: "USD",
+    CA: "CAD",
+  });
+});
diff --git a/Sprint-2/implement/querystring.js b/Sprint-2/implement/querystring.js
index 45ec4e5f3..86a731a29 100644
--- a/Sprint-2/implement/querystring.js
+++ b/Sprint-2/implement/querystring.js
@@ -6,11 +6,35 @@ function parseQueryString(queryString) {
   const keyValuePairs = queryString.split("&");
 
   for (const pair of keyValuePairs) {
-    const [key, value] = pair.split("=");
-    queryParams[key] = value;
+    if (!pair) continue;
+    const equalIndex = pair.indexOf("=");
+    if (equalIndex === -1) {
+      const key = pair;
+      queryParams[decodeURIComponent(key) ?? ""] = "";
+      continue;
+    }
+
+    let key = pair.substring(0, equalIndex).replace("+", " ");
+    let value = pair.substring(equalIndex + 1).replace("+", " ");
+
+    key = decodeURIComponent(key);
+    value = decodeURIComponent(value);
+    if (queryParams[key] !== undefined) {
+      if (Array.isArray(queryParams[key])) {
+        queryParams[key].push(value);
+      } else {
+        queryParams[key] = [queryParams[key], value];
+      }
+    } else {
+      queryParams[key] = value;
+    }
   }
 
   return queryParams;
 }
 
+console.log(parseQueryString("=value"));
+console.log(parseQueryString("key"));
+console.log(parseQueryString("key="));
+console.log(parseQueryString("="));
 module.exports = parseQueryString;
diff --git a/Sprint-2/implement/querystring.test.js b/Sprint-2/implement/querystring.test.js
index 328b8df61..e9e0e9abd 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({
diff --git a/Sprint-2/implement/tally.js b/Sprint-2/implement/tally.js
index f47321812..f0da8bc2e 100644
--- a/Sprint-2/implement/tally.js
+++ b/Sprint-2/implement/tally.js
@@ -1,3 +1,16 @@
-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..61bc2ce6d 100644
--- a/Sprint-2/implement/tally.test.js
+++ b/Sprint-2/implement/tally.test.js
@@ -19,16 +19,33 @@ 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
+test("tally on an array returns an object containing the count for each unique item", () => {
+  const items = ["a", "b", "c"];
+  const expected = { a: 1, b: 1, c: 1 };
+  expect(tally(items)).toEqual(expected);
+});
 
 // 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", () => {
+  const items = [];
+  const expected = {};
+  expect(tally(items)).toEqual(expected);
+});
 
 // Given an array with duplicate items
 // When passed to tally
 // Then it should return counts for each unique item
+test("tally on an array with duplicate items returns counts for each unique item", () => {
+  const items = ["a", "a", "a"];
+  const expected = { a: 3 };
+  expect(tally(items)).toEqual(expected);
+});
 
 // Given an invalid input like a string
 // When passed to tally
 // Then it should throw an error
+test("tally on an invalid input like a string throws an error", () => {
+  expect(() => tally("a")).toThrow("Input must be an array");
+});
diff --git a/Sprint-2/interpret/invert.js b/Sprint-2/interpret/invert.js
index bb353fb1f..3f1ca0dd4 100644
--- a/Sprint-2/interpret/invert.js
+++ b/Sprint-2/interpret/invert.js
@@ -6,24 +6,38 @@
 
 // E.g. invert({x : 10, y : 20}), target output: {"10": "x", "20": "y"}
 
-function invert(obj) {
-  const invertedObj = {};
+// function invert(obj) {
+//   const invertedObj = {};
 
-  for (const [key, value] of Object.entries(obj)) {
-    invertedObj.key = value;
-  }
+//   for (const [key, value] of Object.entries(obj)) {
+//     invertedObj.key = value;
+//   }
 
-  return invertedObj;
-}
+//   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?
-
+// It returns an array of key-value pairs.
+// It's needed because it allows us to iterate over the keys and values of the object.
 // d) Explain why the current return value is different from the target output
+// In line 9 we are assigning the value to the key "key" instead of the value of the key variable.
 
 // e) Fix the implementation of invert (and write tests to prove it's fixed!)
+
+function invert(obj) {
+  const invertedObj = {};
+
+  for (const [key, value] of Object.entries(obj)) {
+    invertedObj[value] = key;
+  }
+
+  return invertedObj;
+}
+
+module.exports = invert;
diff --git a/Sprint-2/interpret/invert.test.js b/Sprint-2/interpret/invert.test.js
new file mode 100644
index 000000000..433c9a72a
--- /dev/null
+++ b/Sprint-2/interpret/invert.test.js
@@ -0,0 +1,24 @@
+const invert = require("./invert");
+
+// 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"}
+
+describe("invert", () => {
+  it("should swap the keys and values in an object", () => {
+    expect(invert({ a: 1, b: 2 })).toEqual({ 1: "a", 2: "b" });
+    expect(invert({ a: 1 })).toEqual({ 1: "a" });
+    expect(invert({ x: 10, y: 20 })).toEqual({ 10: "x", 20: "y" });
+    expect(invert({ name: "Tom", age: 30 })).toEqual({
+      Tom: "name",
+      30: "age",
+    });
+  });
+
+  it("should handle empty objects", () => {
+    expect(invert({})).toEqual({});
+  });
+});