diff --git a/Sprint-2/1-key-errors/0.js b/Sprint-2/1-key-errors/0.js
index 653d6f5a0..9ea982a1d 100644
--- a/Sprint-2/1-key-errors/0.js
+++ b/Sprint-2/1-key-errors/0.js
@@ -1,13 +1,29 @@
 // Predict and explain first...
 //  =============> write your prediction here
+// I guess the function is trying to capitalise the first letter of the string,
+// capture the rest of the string from index 1 to the end of the string,
+// and concatenate them together to return the capitalised string
 
 // call the function capitalise with a string input
 // interpret the error message and figure out why an error is occurring
-
+/*
 function capitalise(str) {
   let str = `${str[0].toUpperCase()}${str.slice(1)}`;
   return str;
 }
+*/
 
 // =============> write your explanation here
+// After calling the function capitalise with a string input,
+// I got a syntax error that "str" has already been declared.
+// This is because str has already been declared as a parameter of the function,
+// when a new variable named str, it causes a conflict.
+
 // =============> write your new code here
+// I renamed the new variable to capitalisedStr to avoid the conflict
+
+function capitalise(str) {
+  let capitalisedStr = `${str[0].toUpperCase()}${str.slice(1)}`;
+  return capitalisedStr;
+}
+console.log(capitalise("hello")); // should return "Hello"
diff --git a/Sprint-2/1-key-errors/1.js b/Sprint-2/1-key-errors/1.js
index f2d56151f..66c66fb06 100644
--- a/Sprint-2/1-key-errors/1.js
+++ b/Sprint-2/1-key-errors/1.js
@@ -1,10 +1,18 @@
 // Predict and explain first...
+// At the first glance, I believe the function would occur errors because the variable decimalNumber is declared twice.
+// Besides, console.log is trying to log a variable that is not defined in global scope.
 
 // Why will an error occur when this program runs?
 // =============> write your prediction here
+// The first error should be a syntax error that "decimalNumber" has already been declared.
+// Since decimalNumber is declared as a parameter of the function,
+// when a new variable also named decimalNumber is declared inside the function,
+// it causes a conflict.
 
-// Try playing computer with the example to work out what is going on
+// The second error should be a reference error that "decimalNumber is not defined".
 
+// Try playing computer with the example to work out what is going on
+/*
 function convertToPercentage(decimalNumber) {
   const decimalNumber = 0.5;
   const percentage = `${decimalNumber * 100}%`;
@@ -13,8 +21,19 @@ function convertToPercentage(decimalNumber) {
 }
 
 console.log(decimalNumber);
+*/
 
 // =============> write your explanation here
+// After running the code, I got a syntax error that "decimalNumber" has already been declared.
+// I also found out that the decimalNumber inside the function should be declared again.
+// Besides, if we want to log the result of the function, we should call the function with an argument inside console.log().
 
 // Finally, correct the code to fix the problem
 // =============> write your new code here
+function convertToPercentage(decimalNumber) {
+  const percentage = `${decimalNumber * 100}%`;
+
+  return percentage;
+}
+console.log(convertToPercentage(0.5)); // should return "50%"
+console.log(convertToPercentage(0.75)); // should return "75%"
diff --git a/Sprint-2/1-key-errors/2.js b/Sprint-2/1-key-errors/2.js
index aad57f7cf..a446c3882 100644
--- a/Sprint-2/1-key-errors/2.js
+++ b/Sprint-2/1-key-errors/2.js
@@ -1,20 +1,27 @@
-
 // Predict and explain first BEFORE you run any code...
 
 // this function should square any number but instead we're going to get an error
 
 // =============> write your prediction of the error here
-
+// I guess the error is a reference error because the parameter is not defined correctly.
+/*
 function square(3) {
     return num * num;
 }
-
+*/
 // =============> write the error message here
+// function square(3) {
+//                 ^
+//SyntaxError: Unexpected number
+// In fact, the error is a syntax error because number 3 is unexpected here.
 
 // =============> explain this error message here
+// Number 3 is not a valid parameter name, which is misplacing and causes a syntax error.
 
 // Finally, correct the code to fix the problem
 
 // =============> write your new code here
-
-
+function square(num) {
+  return num * num;
+}
+console.log(square(3)); // should return 9
diff --git a/Sprint-2/2-mandatory-debug/0.js b/Sprint-2/2-mandatory-debug/0.js
index b27511b41..5eb351210 100644
--- a/Sprint-2/2-mandatory-debug/0.js
+++ b/Sprint-2/2-mandatory-debug/0.js
@@ -1,14 +1,24 @@
 // Predict and explain first...
 
 // =============> write your prediction here
-
+// It seems the function multiply did not return any value.
+// Therefore, it is like a console.log returning undefined, while it is inside another console.log.
+// So the output should be "The result of multiplying 10 and 32 is undefined".
+/*
 function multiply(a, b) {
   console.log(a * b);
 }
 
 console.log(`The result of multiplying 10 and 32 is ${multiply(10, 32)}`);
-
+*/
 // =============> write your explanation here
+// After running the code, I got a separate output of 320 and "The result of multiplying 10 and 32 is undefined".
+// This is because the function multiply does not return any value, so it returns undefined by default.
+// The console.log inside the function multiply prints 320 when the function is called.
 
 // Finally, correct the code to fix the problem
 //  =============> write your new code here
+function multiply(a, b) {
+  return a * b;
+}
+console.log(`The result of multiplying 10 and 32 is ${multiply(10, 32)}`); // should return "The result of multiplying 10 and 32 is 320"
diff --git a/Sprint-2/2-mandatory-debug/1.js b/Sprint-2/2-mandatory-debug/1.js
index 37cedfbcf..f5f433d79 100644
--- a/Sprint-2/2-mandatory-debug/1.js
+++ b/Sprint-2/2-mandatory-debug/1.js
@@ -1,13 +1,23 @@
 // Predict and explain first...
 //  =============> write your prediction here
+// It looks like the function sum return nothing because a+b is written in the next line after return statement.
+// Therefore, the output should be "The sum of 10 and 32 is undefined".
 
+/*
 function sum(a, b) {
   return;
   a + b;
 }
 
 console.log(`The sum of 10 and 32 is ${sum(10, 32)}`);
-
+*/
 // =============> write your explanation here
+// After running the code, I got "The sum of 10 and 32 is undefined".
+// The return statement ends the function execution and a+b is never evaluated.
+
 // Finally, correct the code to fix the problem
 //  =============> write your new code here
+function sum(a, b) {
+  return a + b;
+}
+console.log(`The sum of 10 and 32 is ${sum(10, 32)}`); // should return "The sum of 10 and 32 is 42"
diff --git a/Sprint-2/2-mandatory-debug/2.js b/Sprint-2/2-mandatory-debug/2.js
index 57d3f5dc3..8c2afa56a 100644
--- a/Sprint-2/2-mandatory-debug/2.js
+++ b/Sprint-2/2-mandatory-debug/2.js
@@ -2,9 +2,11 @@
 
 // Predict the output of the following code:
 // =============> Write your prediction here
+// The output should always be 3 because the parameter is not defined in the function,
+// and the variable num is always 103 in the global scope.
 
 const num = 103;
-
+/*
 function getLastDigit() {
   return num.toString().slice(-1);
 }
@@ -12,13 +14,30 @@ function getLastDigit() {
 console.log(`The last digit of 42 is ${getLastDigit(42)}`);
 console.log(`The last digit of 105 is ${getLastDigit(105)}`);
 console.log(`The last digit of 806 is ${getLastDigit(806)}`);
-
+*/
 // Now run the code and compare the output to your prediction
 // =============> write the output here
+/*
+The last digit of 42 is 3
+The last digit of 105 is 3
+The last digit of 806 is 3
+*/
+// As expected, the output is always 3.
+
 // Explain why the output is the way it is
 // =============> write your explanation here
+//The num is defined in the global scope as 103.
+// And the function does not accept any parameters.
+// So every time the function is called, it returns the last digit of 103, which is 3.
+
 // Finally, correct the code to fix the problem
 // =============> write your new code here
+function getLastDigit(num) {
+  return num.toString().slice(-1);
+}
+console.log(`The last digit of 42 is ${getLastDigit(42)}`); // should return 2
+console.log(`The last digit of 105 is ${getLastDigit(105)}`); // should return 5
+console.log(`The last digit of 806 is ${getLastDigit(806)}`); // should return 6
 
 // This program should tell the user the last digit of each number.
 // Explain why getLastDigit is not working properly - correct the problem
diff --git a/Sprint-2/3-mandatory-implement/1-bmi.js b/Sprint-2/3-mandatory-implement/1-bmi.js
index 17b1cbde1..fba0a98b7 100644
--- a/Sprint-2/3-mandatory-implement/1-bmi.js
+++ b/Sprint-2/3-mandatory-implement/1-bmi.js
@@ -15,5 +15,9 @@
 // It should return their Body Mass Index to 1 decimal place
 
 function calculateBMI(weight, height) {
-    // return the BMI of someone based off their weight and height
-}
\ No newline at end of file
+  // return the BMI of someone based off their weight and height
+  const bmi = weight / (height * height);
+  return bmi.toFixed(1);
+}
+
+console.log(calculateBMI(70, 1.73)); // should return 23.4
diff --git a/Sprint-2/3-mandatory-implement/2-cases.js b/Sprint-2/3-mandatory-implement/2-cases.js
index 5b0ef77ad..f1d549e32 100644
--- a/Sprint-2/3-mandatory-implement/2-cases.js
+++ b/Sprint-2/3-mandatory-implement/2-cases.js
@@ -14,3 +14,11 @@
 // You will need to come up with an appropriate name for the function
 // Use the MDN string documentation to help you find a solution
 // This might help https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/toUpperCase
+
+function toUpperSnakeCase(str) {
+  // return the string in UPPER_SNAKE_CASE
+  return str.toUpperCase().replaceAll(" ", "_");
+}
+
+console.log(toUpperSnakeCase("hello there")); // should return "HELLO_THERE"
+console.log(toUpperSnakeCase("lord of the rings")); // should return "LORD_OF_THE_RINGS"
diff --git a/Sprint-2/3-mandatory-implement/3-to-pounds.js b/Sprint-2/3-mandatory-implement/3-to-pounds.js
index 6265a1a70..0b87c9185 100644
--- a/Sprint-2/3-mandatory-implement/3-to-pounds.js
+++ b/Sprint-2/3-mandatory-implement/3-to-pounds.js
@@ -4,3 +4,64 @@
 // You will need to declare a function called toPounds with an appropriately named parameter.
 
 // You should call this function a number of times to check it works for different inputs
+
+/* Code from Sprint-1 below for reference
+const penceString = "399p";
+
+const penceStringWithoutTrailingP = penceString.substring(
+  0,
+  penceString.length - 1
+);
+
+const paddedPenceNumberString = penceStringWithoutTrailingP.padStart(3, "0");
+const pounds = paddedPenceNumberString.substring(
+  0,
+  paddedPenceNumberString.length - 2
+);
+
+const pence = paddedPenceNumberString
+  .substring(paddedPenceNumberString.length - 2)
+  .padEnd(2, "0");
+
+console.log(`£${pounds}.${pence}`);
+*/
+
+function toPounds(penceString) {
+  if (typeof penceString !== "string" || !penceString.endsWith("p")) {
+    console.log("Invalid input, please provide a penceString ending with 'p'");
+    return "Invalid input, please provide a penceString ending with 'p'";
+  }
+
+  const penceStringWithoutTrailingP = penceString.substring(
+    0,
+    penceString.length - 1
+  );
+
+  if (Number.isNaN(Number(penceStringWithoutTrailingP))) {
+    console.log("Invalid input, please provide a numeric penceString");
+    return "Invalid input, please provide a numeric penceString";
+  }
+
+  const paddedPenceNumberString = penceStringWithoutTrailingP.padStart(3, "0");
+  const pounds = paddedPenceNumberString.substring(
+    0,
+    paddedPenceNumberString.length - 2
+  );
+
+  const pence = paddedPenceNumberString
+    .substring(paddedPenceNumberString.length - 2)
+    .padEnd(2, "0");
+
+  console.log(`£${pounds}.${pence}`);
+  return `£${pounds}.${pence}`;
+}
+
+toPounds("399p");
+toPounds("5p");
+toPounds("89p");
+toPounds("1234p");
+toPounds("0p");
+toPounds("70000p");
+toPounds("abcp");
+toPounds(500);
+toPounds("abc");
diff --git a/Sprint-2/4-mandatory-interpret/time-format.js b/Sprint-2/4-mandatory-interpret/time-format.js
index 7c98eb0e8..833f85de0 100644
--- a/Sprint-2/4-mandatory-interpret/time-format.js
+++ b/Sprint-2/4-mandatory-interpret/time-format.js
@@ -1,4 +1,11 @@
+let timesToBeCalled = 0;
+
 function pad(num) {
+  timesToBeCalled += 1;
+  console.log(
+    ` Pad has been called ${timesToBeCalled} times and num is ${num}`
+  );
+  console.log(` The return value will be ${num.toString().padStart(2, "0")}`);
   return num.toString().padStart(2, "0");
 }
 
@@ -11,6 +18,8 @@ function formatTimeDisplay(seconds) {
   return `${pad(totalHours)}:${pad(remainingMinutes)}:${pad(remainingSeconds)}`;
 }
 
+console.log(formatTimeDisplay(61));
+
 // You will need to play computer with this example - use the Python Visualiser https://pythontutor.com/visualize.html#mode=edit
 // to help you answer these questions
 
@@ -18,17 +27,27 @@ function formatTimeDisplay(seconds) {
 
 // a) When formatTimeDisplay is called how many times will pad be called?
 // =============> write your answer here
+// The pad function will be called 3 times when formatTimeDisplay is called.
+// 1st: for totalHours
+// 2nd: for remainingMinutes
+// 3rd: for remainingSeconds
 
 // Call formatTimeDisplay with an input of 61, now answer the following:
 
 // b) What is the value assigned to num when pad is called for the first time?
 // =============> write your answer here
+// The value assigned to num is 0 when pad is called for the first time because 61 seconds is 0 hours, 1 minute, and 1 second.
 
 // c) What is the return value of pad is called for the first time?
 // =============> write your answer here
+// The return value of pad is "00" in string format because 0 is padded to 2 digits with leading zeros.
 
 // d) What is the value assigned to num when pad is called for the last time in this program?  Explain your answer
 // =============> write your answer here
+// The value assigned to num is 1 when pad is called for the last time.
+// It is because the remaining seconds is 1 second after taken 60 seconds for 1 minute.
 
 // e) What is the return value assigned to num when pad is called for the last time in this program?  Explain your answer
 // =============> write your answer here
+// The return value assigned to num is "01" in string format.
+// It is because 1 second is padded to 2 digits with a leading zero.
diff --git a/Sprint-2/5-stretch-extend/format-time.js b/Sprint-2/5-stretch-extend/format-time.js
index 32a32e66b..dd08a082b 100644
--- a/Sprint-2/5-stretch-extend/format-time.js
+++ b/Sprint-2/5-stretch-extend/format-time.js
@@ -4,22 +4,139 @@
 
 function formatAs12HourClock(time) {
   const hours = Number(time.slice(0, 2));
+  const minutes = Number(time.slice(3));
+  if (isNaN(hours) || isNaN(minutes)) {
+    throw new Error("Invalid time");
+  }
+  if (hours < 0 || hours > 24 || minutes < 0 || minutes > 59) {
+    throw new Error("Invalid time");
+  }
+  if (time[2] !== ":") {
+    throw new Error("Invalid time");
+  }
+  if (time.length !== 5) {
+    throw new Error("Invalid time");
+  }
+
+  const minutesStr = String(minutes).padStart(2, 0);
+
+  if (hours == 0) {
+    return `12:${minutesStr} am`;
+  }
+
+  if (hours == 12 && minutes >= 0) {
+    return `12:${minutesStr} pm`;
+  }
+
+  if (hours == 24) {
+    return `12:${minutesStr} am`;
+  }
+
   if (hours > 12) {
-    return `${hours - 12}:00 pm`;
+    return `${String(hours - 12).padStart(2, 0)}:${minutesStr} pm`;
   }
+
   return `${time} am`;
 }
 
-const currentOutput = formatAs12HourClock("08:00");
-const targetOutput = "08:00 am";
+const currentOutput = formatAs12HourClock("08:01");
+const targetOutput = "08:01 am";
 console.assert(
   currentOutput === targetOutput,
   `current output: ${currentOutput}, target output: ${targetOutput}`
 );
 
-const currentOutput2 = formatAs12HourClock("23:00");
-const targetOutput2 = "11:00 pm";
+const currentOutput2 = formatAs12HourClock("23:09");
+const targetOutput2 = "11:09 pm";
 console.assert(
   currentOutput2 === targetOutput2,
   `current output: ${currentOutput2}, target output: ${targetOutput2}`
 );
+
+const currentOutput3 = formatAs12HourClock("12:00");
+const targetOutput3 = "12:00 pm";
+console.assert(
+  currentOutput3 === targetOutput3,
+  `current output: ${currentOutput3}, target output: ${targetOutput3}`
+);
+
+const currentOutput4 = formatAs12HourClock("00:00");
+const targetOutput4 = "12:00 am";
+console.assert(
+  currentOutput4 === targetOutput4,
+  `current output: ${currentOutput4}, target output: ${targetOutput4}`
+);
+
+const currentOutput5 = formatAs12HourClock("15:30");
+const targetOutput5 = "03:30 pm";
+console.assert(
+  currentOutput5 === targetOutput5,
+  `current output: ${currentOutput5}, target output: ${targetOutput5}`
+);
+
+const currentOutput6 = formatAs12HourClock("11:15");
+const targetOutput6 = "11:15 am";
+console.assert(
+  currentOutput6 === targetOutput6,
+  `current output: ${currentOutput6}, target output: ${targetOutput6}`
+);
+
+const currentOutput7 = formatAs12HourClock("00:30");
+const targetOutput7 = "12:30 am";
+console.assert(
+  currentOutput7 === targetOutput7,
+  `current output: ${currentOutput7}, target output: ${targetOutput7}`
+);
+
+const currentOutput8 = formatAs12HourClock("12:45");
+const targetOutput8 = "12:45 pm";
+console.assert(
+  currentOutput8 === targetOutput8,
+  `current output: ${currentOutput8}, target output: ${targetOutput8}`
+);
+
+const currentOutput9 = formatAs12HourClock("24:00");
+const targetOutput9 = "12:00 am";
+console.assert(
+  currentOutput9 === targetOutput9,
+  `current output: ${currentOutput9}, target output: ${targetOutput9}`
+);
+
+const currentOutput10 = formatAs12HourClock("24:05");
+const targetOutput10 = "12:05 am";
+console.assert(
+  currentOutput10 === targetOutput10,
+  `current output: ${currentOutput10}, target output: ${targetOutput10}`
+);
+
+// Edge cases and invalid inputs
+
+try {
+  formatAs12HourClock("25:00");
+  console.assert(false, "Expected an error for invalid hours");
+} catch (e) {
+  console.assert(
+    e.message === "Invalid time",
+    `Unexpected error message: ${e.message}`
+  );
+}
+
+try {
+  formatAs12HourClock("10:60");
+  console.assert(false, "Expected an error for invalid minutes");
+} catch (e) {
+  console.assert(
+    e.message === "Invalid time",
+    `Unexpected error message: ${e.message}`
+  );
+}
+
+try {
+  formatAs12HourClock("ab:cd");
+  console.assert(false, "Expected an error for non-numeric input");
+} catch (e) {
+  console.assert(
+    e.message === "Invalid time",
+    `Unexpected error message: ${e.message}`
+  );
+}