diff --git a/README.md b/README.md
index a670384e..fbb43c48 100644
--- a/README.md
+++ b/README.md
@@ -20,6 +20,7 @@ Read [CONTRIBUTING.md](./CONTRIBUTING.md) for contribution guidelines.
 1. [Day 1 -- The Fizz Buzz Problem](./Day1/) -- [http://codetoexpress.tech/dc/day1](http://codetoexpress.tech/dc/day1)
 2. [Day 2 -- String Reversal + Palindrome](./Day2/) -- [http://codetoexpress.tech/dc/day2/](http://codetoexpress.tech/dc/day2)
 3. [Day 3 -- The Hamming Distance Problem](./Day3/) -- [http://codetoexpress.tech/dc/day3/](http://codetoexpress.tech/dc/day3/)
+4. [Day 4 -- Num Vowels + Max Chars](./day4/) -- [http://codetoexpress.tech/dc/day4/](http://codetoexpress.tech/dc/day4/)
 
 ## Timeline
 
diff --git a/day4/Java/NumVowels.java b/day4/Java/NumVowels.java
new file mode 100644
index 00000000..964e573c
--- /dev/null
+++ b/day4/Java/NumVowels.java
@@ -0,0 +1,33 @@
+import java.util.Scanner;
+
+public class NumVowels {
+    public static void main (String[] args) {
+        // set count = 0
+        int count = 0;
+
+        // Input the string
+        Scanner input = new Scanner(System.in);
+        System.out.println("/* ===== Number of Vowels ===== */");
+        System.out.print("\nEnter the string: ");
+        String str = input.next();
+
+        // Convert input string to lower case
+        str = str.toLowerCase();
+
+        // Run a loop from 0 to string length
+        for (int i=0; i<str.length(); i++) {
+            if (
+                str.charAt(i) == 'a' ||
+                str.charAt(i) == 'e' ||
+                str.charAt(i) == 'i' ||
+                str.charAt(i) == 'o' ||
+                str.charAt(i) == 'u'
+            ) {
+                count++;
+            }
+        }
+
+        // Print the result
+        System.out.println("Number of vowels in \"" + str + "\" = " + count);
+    }
+}
\ No newline at end of file
diff --git a/day4/Java/NumVowels2.java b/day4/Java/NumVowels2.java
new file mode 100644
index 00000000..8ae42cf5
--- /dev/null
+++ b/day4/Java/NumVowels2.java
@@ -0,0 +1,34 @@
+import java.util.Scanner;
+
+public class NumVowels2 {
+    public static void main (String[] args) {
+        // set count = 0
+        int count = 0;
+
+        // Input the string
+        Scanner input = new Scanner(System.in);
+        System.out.println("/* ===== Number of Vowels ===== */");
+        System.out.print("\nEnter the string: ");
+        String str = input.next();
+
+        // Convert input string to lower case
+        str = str.toLowerCase();
+
+        // Create an array of vowels
+        char[] vowels = new char[]{ 'a', 'e', 'i', 'o', 'u' };
+
+        // Run a loop from 0 to string length
+        for (int i=0; i<str.length(); i++) {
+            // Check whether the current character exists in the vowels array
+            for (int j=0; j<5; j++) {
+                if (str.charAt(i) == vowels[j]) {
+                    count++;
+                    break;
+                }
+            }
+        }
+
+        // Print the result
+        System.out.println("Number of vowels in \"" + str + "\" = " + count);
+    }
+}
\ No newline at end of file
diff --git a/day4/JavaScript/partA_sol1.js b/day4/JavaScript/partA_sol1.js
new file mode 100644
index 00000000..12322e0a
--- /dev/null
+++ b/day4/JavaScript/partA_sol1.js
@@ -0,0 +1,25 @@
+// Step 1: Set count = 0
+// Step 2: Run a loop from i=0 to i=string_length
+// Step 3: In each iteration check whether the character at position i is ‘a’, ‘e’, ‘i’, ‘o’, or ‘u’. If the condition passes, increment the value of count.
+// Step 4: Print and return the results.
+
+function numVowels (str) {
+    let count = 0;
+
+    for (let i=0; i<str.length; i++) {
+        if (
+            str[i].toLowerCase() === 'a' ||
+            str[i].toLowerCase() === 'e' ||
+            str[i].toLowerCase() === 'i' ||
+            str[i].toLowerCase() === 'o' ||
+            str[i].toLowerCase() === 'u' 
+        ) {
+            count++;
+        }
+    }
+
+    console.log (`The number of vowels in ${str} is = ${count}`);
+}
+
+numVowels ('hello');
+numVowels ('Greetings');
\ No newline at end of file
diff --git a/day4/JavaScript/partA_sol2.js b/day4/JavaScript/partA_sol2.js
new file mode 100644
index 00000000..05e0b583
--- /dev/null
+++ b/day4/JavaScript/partA_sol2.js
@@ -0,0 +1,23 @@
+// Step 1: Set count = 0
+// Step 2: Store the vowels in an array (say, vowels)
+// Step 3: Run a loop from i=0 to i=string_length
+// Step 4: In each iteration check whether the current character (at position i) of the string is there in the vowels array using indexOf() method
+// Step 5: Increment the count if the above condition is satisfied.
+// Step 6: Print the result
+
+function numVowels (str) {
+    let count = 0;
+    let vowels = ['a', 'e', 'i', 'o', 'u'];
+
+    // Iterate  over each character in the string
+    for (let i=0; i<str.length; i++) {
+        if (vowels.indexOf(str[i].toLowerCase()) > 0) {
+            count++;
+        }
+    }
+
+    console.log (`The number of vowels in ${str} is = ${count}`);
+}
+
+numVowels ('hello');
+numVowels ('Greetings');
\ No newline at end of file
diff --git a/day4/JavaScript/partA_sol3.js b/day4/JavaScript/partA_sol3.js
new file mode 100644
index 00000000..6ef3cc9b
--- /dev/null
+++ b/day4/JavaScript/partA_sol3.js
@@ -0,0 +1,22 @@
+// Step 1: Set count = 0
+// Step 2: Store the vowels in an array (say, vowels)
+// Step 3: Run a loop from i=0 to i=string_length
+// Step 4: In each iteration, run a nested loop from j=0 to j<5 (5 vowels), and check whether string[i] exists in vowels[j].
+// Step 5: Increment the count if the above condition is satisfied.
+// Step 6: Print the result
+
+function numVowels (str) {
+    let count = 0;
+    let vowels = ['a', 'e', 'i', 'o', 'u'];
+
+    for (let char of str) {
+        for (let vowel of vowels) {
+            if (char.toLowerCase() === vowel)  count++;
+        }
+    }
+
+    console.log (`The number of vowels in ${str} is = ${count}`);
+}
+
+numVowels ('hello');
+numVowels ('Greetings');
\ No newline at end of file
diff --git a/day4/JavaScript/partA_sol4.js b/day4/JavaScript/partA_sol4.js
new file mode 100644
index 00000000..a13adee7
--- /dev/null
+++ b/day4/JavaScript/partA_sol4.js
@@ -0,0 +1,36 @@
+// Step 1: Set count = 0
+// Step 2: Store the vowels in an object (vowels) with initial values as zero
+// Step 3: Iterate through each character of string and check whether it exists in the vowels object
+// Step 4: If it exists, increment its value, and the value of count variable
+// Step 5: Print the result
+
+function numVowels (str) {
+    let count = 0;
+    let vowels = {
+        'a': 0,
+        'e': 0,
+        'i': 0,
+        'o': 0,
+        'u': 0
+    };
+
+    for (let char of str) {
+        // if (vowels[char]) {
+        //     vowels [char]++;
+        //     count++;
+        // }
+
+        for (vowel in vowels) {
+            if (char.toLowerCase() === vowel) {
+                count++;
+                vowels[vowel]++
+            }
+        }
+    }
+
+    console.log (`The number of vowels in ${str} is = ${count}`);
+
+}
+
+numVowels ('hello');
+numVowels ('Greetings');
\ No newline at end of file
diff --git a/day4/JavaScript/partB_sol1.js b/day4/JavaScript/partB_sol1.js
new file mode 100644
index 00000000..73ea456f
--- /dev/null
+++ b/day4/JavaScript/partB_sol1.js
@@ -0,0 +1,37 @@
+// Step 1: Declare an empty object letterCount which will store characters as keys and their frequencies as values.
+// Step 2: Iterate through each character of input string and add it to the object if it doesn't already exist, else increment its’s value
+// Step 3: Find the key with maximum value in the letterCount object.
+
+function maxChars (str) {
+    let letterCount = {};
+
+    // Complete the letter count object
+    for(let currentChar of str) {
+        let flag = 0;
+        for (letter in letterCount) {
+            if (currentChar.toLowerCase() === letter) {
+                flag = 1;
+                letterCount[letter]++;
+            }
+        }
+
+        if (flag === 0) {
+            letterCount[currentChar] = 1;
+        }
+    }
+
+    // Find the maximum value key from the letterCount
+    let max = 0, maxChar = '';
+    for (letter in letterCount) {
+        if (letterCount[letter] >= max) {
+            max = letterCount[letter];
+            maxChar = letter;
+        }
+    }
+
+    // Print the result
+    console.log(`The maximum frequency letter is: "${maxChar}" and it appears ${letterCount[maxChar]} number of times!`);
+    return letterCount[maxChar];
+}
+
+maxChars('helllllo worlld');
\ No newline at end of file
diff --git a/day4/JavaScript/partB_sol2.js b/day4/JavaScript/partB_sol2.js
new file mode 100644
index 00000000..6923e783
--- /dev/null
+++ b/day4/JavaScript/partB_sol2.js
@@ -0,0 +1,27 @@
+// Answer similar to first solution, but Step 2 has been replaced by a one liner
+
+function maxChars (sentence) {
+    let characters = {};
+
+    // Update characters object with count of each character in sentence
+    for (let letter of sentence) {
+        // increment the count of existing letter OR add the new character with value = 1
+        characters[letter] = characters[letter] + 1 || 1;
+    }
+
+    let max = 0,
+      maxChar = '';
+
+    for (let character in characters) {
+        if (max < characters[character]) {
+            max = characters[character];
+            maxChar = character;
+        }
+    }
+
+    // Print the result
+    console.log(`The maximum frequency letter is: "${maxChar}" and it appears ${characters[maxChar]} number of times!`);
+    return characters[maxChar];    
+}
+
+maxChars('helllllo worlld');
\ No newline at end of file
diff --git a/day4/README.md b/day4/README.md
new file mode 100644
index 00000000..552721f5
--- /dev/null
+++ b/day4/README.md
@@ -0,0 +1,293 @@
+# Day 4 -- Number of Vowels and Max Chars
+
+![cover](./cover.png)
+
+## Part A -- Number of Vowels
+
+**Question** - Given a string, Write a program that prints the number of vowels in it.
+
+## JavaScript Implementation
+
+### [Solution 1](./JavaScript/partA_sol1.js)
+
+```js
+function numVowels (str) {
+    let count = 0;
+
+    // Iterate over each character in the string
+    for (let i=0; i<str.length; i++) {
+        // check whether this character (in lower case) is a, e, i, o, or u (converting in lower case would reduce the amount of conditons by half since there would be no need to check A, E, I, O or U)
+        if (
+            str[i].toLowerCase() === 'a' ||
+            str[i].toLowerCase() === 'e' ||
+            str[i].toLowerCase() === 'i' ||
+            str[i].toLowerCase() === 'o' ||
+            str[i].toLowerCase() === 'u'
+        ) {
+            count++;
+        }
+    }
+
+    // Print and return the number of vowels
+    console.log(`The number of vowels in ${str} is = ${count}`);
+    return count;
+}
+
+numVowels ('hello');
+numVowels ('Greetings');
+```
+
+## [Solution 2](./JavaScript/partA_sol2.js)
+
+```js
+function numVowels (str) {
+    let count = 0;
+
+    // Define a vowels array
+    let vowels = ['a', 'e', 'i', 'o', 'u'];
+
+    // Iterate over each character in the string
+    for (let i=0; i<str.length; i++) {
+        // check whether this character (in lower case) is a, e, i, o, or u (converting in lower case would reduce the amount of conditons by half since there would be no need to check A, E, I, O or U)
+        if (vowels.indexOf(str[i].toLowerCase()) >= 0) {
+            count++;
+        }
+    }
+
+    // Print and return the number of vowels
+    console.log(`The number of vowels in ${str} is = ${count}`);
+    return count;
+}
+
+numVowels ('hEllo');
+numVowels ('Greetings');
+```
+
+## [Solution 3](./JavaScript/partA_sol3.js)
+
+```js
+// Store vowels in an array
+// check each character of the string with each element in vowels array
+
+function numVowels (str) {
+    // Initialize count to be zero
+    let count = 0;
+
+    // Define an array of vowels
+    let vowels = ['a', 'e', 'i', 'o', 'u'];
+
+    // Check each character of string 
+    for (let char of str) {
+        for (let vowel of vowels) {
+            if (char.toLowerCase() === vowel)  count++;
+        }
+    }
+
+    // Print the result
+    console.log(`The number of vowels in "${str}" is = ${count}`);
+    return count;
+}
+
+numVowels ('hello');
+numVowels ('Greetings');
+```
+
+## [Solution 4](./JavaScript/partA_sol4.js)
+
+```js
+// Similar to previous method
+// Instead of storing vowels in an array, store them in an object as keys and values as the number of occurances
+
+function numVowels (str) {
+    console.log('\nString: ', str);
+
+    // Initialize count to be zero
+    let count = 0;
+
+    // Store the vowels in an object
+    let vowels = {
+        'a': 0,
+        'b': 0,
+        'c': 0,
+        'd': 0,
+        'e': 0
+    };
+
+    // Iterate through each character of string to check vowels
+    for (let char of str) {
+        for (vowel in vowels) {
+            if (char.toLowerCase() === vowel) {
+                count++;
+                vowels[vowel]++;
+            }
+        }
+    }
+    
+    // Print the result
+    console.log('Vowel Count: ');
+    for (let vowel in vowels) {
+        console.log(`Vowel: ${vowel} appears ${vowels[vowel]} number of times in the string "${str}"`);
+    }    
+
+    console.log("Total number of vowels: " + count);
+    return count;
+}
+
+numVowels ('hello');
+numVowels ('Greetings');
+```
+
+## Java Implementatio
+
+### [Solution 1](./Java/NumVowels.java)
+
+```java
+import java.util.Scanner;
+
+public class NumVowels {
+    public static void main (String[] args) {
+        // set count = 0
+        int count = 0;
+
+        // Input the string
+        Scanner input = new Scanner(System.in);
+        System.out.println("/* ===== Number of Vowels ===== */");
+        System.out.print("\nEnter the string: ");
+        String str = input.next();
+
+        // Convert input string to lower case
+        str = str.toLowerCase();
+
+        // Run a loop from 0 to string length
+        for (int i=0; i<str.length(); i++) {
+            if (
+                str.charAt(i) == 'a' ||
+                str.charAt(i) == 'e' ||
+                str.charAt(i) == 'i' ||
+                str.charAt(i) == 'o' ||
+                str.charAt(i) == 'u'
+            ) {
+                count++;
+            }
+        }
+
+        // Print the result
+        System.out.println("Number of vowels in \"" + str + "\" = " + count);
+    }
+}
+```
+
+### [Solution 2](./Java/NumVowels2.java)
+
+```java
+import java.util.Scanner;
+
+public class NumVowels2 {
+    public static void main (String[] args) {
+        // set count = 0
+        int count = 0;
+
+        // Input the string
+        Scanner input = new Scanner(System.in);
+        System.out.println("/* ===== Number of Vowels ===== */");
+        System.out.print("\nEnter the string: ");
+        String str = input.next();
+
+        // Convert input string to lower case
+        str = str.toLowerCase();
+
+        // Create an array of vowels
+        char[] vowels = new char[]{ 'a', 'e', 'i', 'o', 'u' };
+
+        // Run a loop from 0 to string length
+        for (int i=0; i<str.length(); i++) {
+            // Check whether the current character exists in the vowels array
+            for (int j=0; j<5; j++) {
+                if (str.charAt(i) == vowels[j]) {
+                    count++;
+                    break;
+                }
+            }
+        }
+
+        // Print the result
+        System.out.println("Number of vowels in \"" + str + "\" = " + count);
+    }
+}
+```
+
+<hr/>
+
+## Part B -- Max Chars Problem
+
+**Question** - Given a string, write a program to return the character that appears most frequently in that string
+
+## JavaScript Implementation
+
+### [Solution 1](./JavaScript/partB_sol1.js)
+
+```js
+function maxChars (str) {
+    let letterCount = {};
+
+    // Complete the letter count object
+    for(let currentChar of str) {
+        let flag = 0;
+        for (letter in letterCount) {
+            if (currentChar.toLowerCase() === letter) {
+                flag = 1;
+                letterCount[letter]++;
+            }
+        }
+
+        if (flag === 0) {
+            letterCount[currentChar] = 1;
+        }
+    }
+
+    // Find the maximum value key from the letterCount
+    let max = 0, maxChar = '';
+    for (letter in letterCount) {
+        if (letterCount[letter] >= max) {
+            max = letterCount[letter];
+            maxChar = letter;
+        }
+    }
+
+    // Print the result
+    console.log(`The maximum frequency letter is: "${maxChar}" and it appears ${letterCount[maxChar]} number of times!`);
+    return letterCount[maxChar];
+}
+
+maxChars('helllllo worlld');
+```
+
+### [Solution 2](./JavaScript/partB_sol2.js)
+
+```js
+function maxChars (sentence) {
+    let characters = {};
+
+    // Update characters object with count of each character in sentence
+    for (let letter of sentence) {
+        // increment the count of existing letter OR add the new character with value = 1
+        characters[letter] = characters[letter] + 1 || 1;
+    }
+
+    let max = 0,
+      maxChar = '';
+
+    for (let character in characters) {
+        if (max < characters[character]) {
+            max = characters[character];
+            maxChar = character;
+        }
+    }
+
+    // Print the result
+    console.log(`The maximum frequency letter is: "${maxChar}" and it appears ${characters[maxChar]} number of times!`);
+    return characters[maxChar];
+}
+
+maxChars('helllllo worlld');
+```
diff --git a/day4/cover.png b/day4/cover.png
new file mode 100644
index 00000000..f76832b6
Binary files /dev/null and b/day4/cover.png differ