diff --git a/ladderz/src/pre_algebra/unit1.rs b/ladderz/src/pre_algebra/unit1.rs
index 2f2b182..227a1e8 100644
--- a/ladderz/src/pre_algebra/unit1.rs
+++ b/ladderz/src/pre_algebra/unit1.rs
@@ -138,8 +138,8 @@ pub fn get_multiples_in_range(n: u32, end: u32) -> HashSet<u32> {
 
 /// Checks if a positive integer `n` is a prime number.
 ///
-/// A prime number is a positive integer greater than 1 that cannot
-/// be evenly divisible by any positive integers other than 1 and itself.
+/// A prime number is a positive integer greater than 1 that is
+/// not evenly divisible by any positive integer other than 1 and itself.
 ///
 /// # Examples
 ///
@@ -168,6 +168,30 @@ pub fn is_prime(n: u32) -> bool {
     true
 }
 
+/// Checks if a positive integer `n` is a composite number.
+///
+/// A composite number is a positive integer that is evenly divisible
+/// by a positive integer other than 1 and itself.
+///
+/// # Examples
+///
+/// ```rust
+/// use ladderz::pre_algebra::is_composite;
+///
+/// assert!(!is_composite(1)); // 1 is not a composite number
+/// assert!(!is_composite(2)); // 2 is not a composite number
+/// assert!(is_composite(4)); // 4 is a composite number
+/// assert!(!is_composite(7)); // 7 is not a composite number
+/// ```
+pub fn is_composite(n: u32) -> bool {
+    for num in 1..n {
+        if n % num == 0 && num != 1 && num != n {
+            return true;
+        }
+    }
+    false
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -240,4 +264,15 @@ mod tests {
         assert!(is_prime(23));
         assert!(!is_prime(9514));
     }
+
+    #[test]
+    fn test_is_composite() {
+        assert!(!is_composite(1));
+        assert!(!is_composite(2));
+        assert!(!is_composite(3));
+        assert!(is_composite(4));
+        assert!(is_composite(8));
+        assert!(is_composite(27));
+        assert!(is_composite(51));
+    }
 }
diff --git a/notebooks/pre-algebra/unit1.ipynb b/notebooks/pre-algebra/unit1.ipynb
index 440942b..44cbd8c 100644
--- a/notebooks/pre-algebra/unit1.ipynb
+++ b/notebooks/pre-algebra/unit1.ipynb
@@ -200,6 +200,15 @@
     "assert get_multiples_in_range(5, 50) == {5, 10, 15, 20, 25, 30, 35, 40, 45, 50}"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Prime and composite numbers\n",
+    "\n",
+    "> [Link to lesson](https://www.khanacademy.org/math/pre-algebra/pre-algebra-factors-multiples/pre-algebra-prime-numbers/v/prime-numbers)."
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},
@@ -215,7 +224,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": 2,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -230,10 +239,46 @@
     "assert is_prime(2) == True\n",
     "assert is_prime(3) == True\n",
     "assert is_prime(4) == False\n",
+    "assert is_prime(7) == True\n",
     "assert is_prime(24) == False\n",
     "assert is_prime(59) == True\n",
     "assert is_prime(72) == False"
    ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**Write a program that determines whether a positive integer `n` is composite.**\n",
+    "\n",
+    "For example for `n = 7`, the output of `is_composite(7)` may be:\n",
+    "\n",
+    "```\n",
+    "False\n",
+    "```"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "def is_composite(n: int) -> bool:\n",
+    "    for num in range(1, n):\n",
+    "        if n % num == 0 and num != 1 and num != n:\n",
+    "            return True\n",
+    "    return False\n",
+    "\n",
+    "assert is_composite(1) == False\n",
+    "assert is_composite(2) == False\n",
+    "assert is_composite(3) == False\n",
+    "assert is_composite(4) == True\n",
+    "assert is_composite(7) == False\n",
+    "assert is_composite(24) == True\n",
+    "assert is_composite(59) == False\n",
+    "assert is_composite(72) == True"
+   ]
   }
  ],
  "metadata": {