diff --git a/Cargo.lock b/Cargo.lock
index 5b36271..412d141 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -736,6 +736,13 @@ dependencies = [
  "windows-sys 0.48.0",
 ]
 
+[[package]]
+name = "mutable-variables"
+version = "0.1.0"
+dependencies = [
+ "syntest",
+]
+
 [[package]]
 name = "native-tls"
 version = "0.2.11"
diff --git a/challenges/challenges.json b/challenges/challenges.json
index ad6bfc8..cd45453 100644
--- a/challenges/challenges.json
+++ b/challenges/challenges.json
@@ -23,6 +23,18 @@
     "created_at": "2024-06-07T00:00:00Z",
     "updated_at": "2024-06-07T00:00:00Z"
   },
+  {
+    "id": 23,
+    "title": "Mutable Variables",
+    "slug": "mutable-variables",
+    "short_description": "Declare and manipulate mutable variables in Rust.",
+    "language": "RUST",
+    "difficulty": "EASY",
+    "track": "RUST_BASICS",
+    "tags": [],
+    "created_at": "2024-06-08T00:00:00Z",
+    "updated_at": "2024-06-08T00:00:00Z"
+  },
   {
     "id": 2,
     "title": "Character counting string",
diff --git a/challenges/mutable-variables/Cargo.toml b/challenges/mutable-variables/Cargo.toml
new file mode 100644
index 0000000..d6f9c90
--- /dev/null
+++ b/challenges/mutable-variables/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "mutable-variables"
+version = "0.1.0"
+edition = "2021"
+
+[dev-dependencies]
+syntest = { path = "../../crates/syntest" }
diff --git a/challenges/mutable-variables/src/lib.rs b/challenges/mutable-variables/src/lib.rs
new file mode 100644
index 0000000..b14afcf
--- /dev/null
+++ b/challenges/mutable-variables/src/lib.rs
@@ -0,0 +1,9 @@
+pub fn manipulate_variables() -> i32 {
+    let mut x = 5;
+    let mut y = 10;
+
+    x += 10;
+    y *= 2;
+
+    x + y
+}
diff --git a/challenges/mutable-variables/src/starter.rs b/challenges/mutable-variables/src/starter.rs
new file mode 100644
index 0000000..e0b33e4
--- /dev/null
+++ b/challenges/mutable-variables/src/starter.rs
@@ -0,0 +1,14 @@
+pub fn manipulate_variables() -> i32 {
+    // Steps:
+    // 1. Declare x as a mutable variable and assign it the value 5
+
+    // 2. Declare y as a mutable variable and assign it the value 10
+
+    // 3. Increment x by 10
+
+    // 4. Multiply y by 2
+
+    // 5. Calculate the sum of x and y
+
+    // 6. Return the calculated sum
+}
diff --git a/challenges/mutable-variables/tests/tests.rs b/challenges/mutable-variables/tests/tests.rs
new file mode 100644
index 0000000..554b12a
--- /dev/null
+++ b/challenges/mutable-variables/tests/tests.rs
@@ -0,0 +1,60 @@
+#[cfg(test)]
+mod tests {
+    use mutable_variables::*;
+    use syntest::{LocalVariable, Mutation, Syntest, Value};
+
+    #[test]
+    fn test_compiles() {
+        manipulate_variables();
+    }
+
+    #[test]
+    fn test_variables() {
+        let syntest = Syntest::from("./src/lib.rs");
+
+        // Expect the 2 variables to exist
+        syntest
+            .variables("manipulate_variables")
+            .iter()
+            .for_each(|var| match var {
+                LocalVariable::Int { .. } => match var.name() {
+                    "x" => {
+                        assert_eq!(
+                            var.value(),
+                            Value::Int(15),
+                            "Expected x to be 15, got {}",
+                            var.value()
+                        );
+                        assert!(var.is_used(), "Expected x to be used");
+                        assert!(var.is_mutable(), "Expected x to be mutable");
+                        assert_eq!(
+                            var.mutations(),
+                            &vec![Mutation::new(Value::Int(5), Value::Int(15))],
+                            "Expected variable x to have a mutation from 5 to 15.",
+                        );
+                    }
+                    "y" => {
+                        assert_eq!(
+                            var.value(),
+                            Value::Int(20),
+                            "Expected y to be 20, got {}",
+                            var.value()
+                        );
+                        assert!(var.is_used(), "Expected y to be used");
+                        assert!(var.is_mutable(), "Expected y to be mutable");
+                        assert_eq!(
+                            var.mutations(),
+                            &vec![Mutation::new(Value::Int(10), Value::Int(20))],
+                            "Expected variable y to have a mutation from 10 to 20."
+                        );
+                    }
+                    _ => {
+                        panic!("Unexpected variable {}", var.name())
+                    }
+                },
+                _ => {
+                    panic!("Expected type to be an integer.")
+                }
+            })
+    }
+}
diff --git a/crates/syntest/src/var.rs b/crates/syntest/src/var.rs
index 5dc901e..cf338ed 100644
--- a/crates/syntest/src/var.rs
+++ b/crates/syntest/src/var.rs
@@ -183,6 +183,12 @@ impl LocalVariable {
     }
 }
 
+impl Display for LocalVariable {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.name())
+    }
+}
+
 #[derive(Debug, PartialEq, Clone)]
 pub enum Value {
     Str(String),
@@ -227,8 +233,23 @@ impl From<Lit> for Value {
     }
 }
 
-impl Display for LocalVariable {
+impl Display for Value {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}", self.name())
+        match self {
+            Value::Str(value) => write!(f, "{}", value),
+            Value::Int(value) => write!(f, "{}", value),
+            Value::Float(value) => write!(f, "{}", value),
+            Value::Char(value) => write!(f, "{}", value),
+            Value::Bool(value) => write!(f, "{}", value),
+            Value::Vec(values) => {
+                write!(f, "[")?;
+                for value in values {
+                    write!(f, "{}, ", value)?;
+                }
+                write!(f, "]")
+            }
+            Value::Closure => write!(f, "closure"),
+            Value::Other => write!(f, "other"),
+        }
     }
 }