diff --git a/week3/Cargo.lock b/week3/Cargo.lock
index d04310f..2942eb8 100644
--- a/week3/Cargo.lock
+++ b/week3/Cargo.lock
@@ -2,6 +2,74 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "getrandom"
+version = "0.2.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c05aeb6a22b8f62540c194aac980f2115af067bfe15a0734d7277a768d396b31"
+dependencies = [
+ "cfg-if",
+ "libc",
+ "wasi",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.139"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "201de327520df007757c1f0adce6e827fe8562fbc28bfd9c15571c66ca1f5f79"
+
+[[package]]
+name = "ppv-lite86"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b40af805b3121feab8a3c29f04d8ad262fa8e0561883e7653e024ae4479e6de"
+
+[[package]]
+name = "rand"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
+dependencies = [
+ "libc",
+ "rand_chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+dependencies = [
+ "ppv-lite86",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_core"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
+dependencies = [
+ "getrandom",
+]
+
+[[package]]
+name = "wasi"
+version = "0.11.0+wasi-snapshot-preview1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c8d87e72b64a3b4db28d11ce29237c246188f4f51057d65a7eab63b7987e423"
+
 [[package]]
 name = "week3"
 version = "0.1.0"
+dependencies = [
+ "rand",
+]
diff --git a/week3/Cargo.toml b/week3/Cargo.toml
index 855ff21..e5a0c5a 100644
--- a/week3/Cargo.toml
+++ b/week3/Cargo.toml
@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+rand = "0.8.5"
diff --git a/week3/src/lib.rs b/week3/src/lib.rs
index 8b13789..0125db4 100644
--- a/week3/src/lib.rs
+++ b/week3/src/lib.rs
@@ -1 +1,67 @@
+use std::any::TypeId;
 
+enum Shape {
+    Circle { radius: f64 },
+    Square { length: f64 },
+    Rectangle { width: f64, height: f64 },
+}
+
+fn area(shape: &Shape) -> f64 {
+    match shape {
+        Shape::Circle { radius } => radius * radius * std::f64::consts::PI,
+        Shape::Square { length } => length * length,
+        Shape::Rectangle { width, height } => width * height,
+    }
+}
+
+#[test]
+fn test_shape_areas() {
+    assert_eq!(area(&Shape::Circle { radius: 1.0 }), std::f64::consts::PI);
+    assert_eq!(area(&Shape::Square { length: 2.0 }), 4.0);
+    assert_eq!(
+        area(&Shape::Rectangle {
+            width: 3.0,
+            height: 8.0
+        }),
+        24.0
+    );
+}
+
+fn random_shape() -> Shape {
+    match rand::random::<i32>() % 3 {
+        0 => Shape::Circle {
+            radius: rand::random(),
+        },
+        1 => Shape::Square {
+            length: rand::random(),
+        },
+        _ => Shape::Rectangle {
+            width: rand::random(),
+            height: rand::random(),
+        },
+    }
+}
+
+fn circle_area(shape: &Shape) -> Option<f64> {
+    if let Shape::Circle { .. } = shape {
+        Option::Some(area(shape))
+    } else {
+        Option::None
+    }
+}
+
+#[test]
+fn test_circle_area() {
+    assert_eq!(
+        circle_area(&Shape::Circle { radius: (1.0) }),
+        Some(std::f64::consts::PI)
+    );
+    assert_eq!(
+        circle_area(&Shape::Rectangle {
+            width: 1.0,
+            height: 1.0
+        }),
+        None
+    );
+    assert_eq!(circle_area(&Shape::Square { length: 1.0 }), None);
+}