diff --git a/exercises/concept/calculator-conundrum/.meta/exemplar.cairo b/exercises/concept/calculator-conundrum/.meta/exemplar.cairo
index 020dd2c9..19f3cdff 100644
--- a/exercises/concept/calculator-conundrum/.meta/exemplar.cairo
+++ b/exercises/concept/calculator-conundrum/.meta/exemplar.cairo
@@ -1,16 +1,15 @@
 #[generate_trait]
 pub impl SimpleCalculatorImpl of SimpleCalculatorTrait {
-    fn calculate(a: i32, b: i32, operation: Option<ByteArray>) -> Result<ByteArray, ByteArray> {
-        let operation = operation.expect('Operation cannot be null');
+    fn calculate(a: i32, b: i32, operation: ByteArray) -> Result<ByteArray, ByteArray> {
+        assert!(operation != "", "Operation cannot be an empty string");
+
         if operation == "+" {
             Result::Ok(format!("{} + {} = {}", a, b, a + b))
         } else if operation == "*" {
             Result::Ok(format!("{} * {} = {}", a, b, a * b))
         } else if operation == "/" {
-            assert!(b != 0, "Division by zero is not allowed");
+            assert(b != 0, 'Division by zero is not allowed');
             Result::Ok(format!("{} / {} = {}", a, b, a / b))
-        } else if operation == "" {
-            Result::Err("Operation cannot be an empty string")
         } else {
             Result::Err("Operation is out of range")
         }
diff --git a/exercises/concept/calculator-conundrum/src/lib.cairo b/exercises/concept/calculator-conundrum/src/lib.cairo
index 7f4ea3d1..d87f391a 100644
--- a/exercises/concept/calculator-conundrum/src/lib.cairo
+++ b/exercises/concept/calculator-conundrum/src/lib.cairo
@@ -1,6 +1,6 @@
 #[generate_trait]
 pub impl SimpleCalculatorImpl of SimpleCalculatorTrait {
-    fn calculate(a: i32, b: i32, operation: Option<ByteArray>) -> Result<ByteArray, ByteArray> {
+    fn calculate(a: i32, b: i32, operation: ByteArray) -> Result<ByteArray, ByteArray> {
         panic!("implement `calculate`")
     }
 }
diff --git a/exercises/concept/calculator-conundrum/tests/calculator_conundrum.cairo b/exercises/concept/calculator-conundrum/tests/calculator_conundrum.cairo
index 53b7a08f..6c0cb948 100644
--- a/exercises/concept/calculator-conundrum/tests/calculator_conundrum.cairo
+++ b/exercises/concept/calculator-conundrum/tests/calculator_conundrum.cairo
@@ -2,76 +2,61 @@ use calculator_conundrum::SimpleCalculatorTrait as SimpleCalculator;
 
 #[test]
 fn addition_with_small_operands() {
-    assert_eq!(SimpleCalculator::calculate(22, 25, Option::Some("+")).unwrap(), "22 + 25 = 47");
+    assert_eq!(SimpleCalculator::calculate(22, 25, "+").unwrap(), "22 + 25 = 47");
 }
 
 #[test]
 #[ignore]
 fn addition_with_large_operands() {
     assert_eq!(
-        SimpleCalculator::calculate(378_961, 399_635, Option::Some("+")).unwrap(),
-        "378961 + 399635 = 778596"
+        SimpleCalculator::calculate(378_961, 399_635, "+").unwrap(), "378961 + 399635 = 778596"
     );
 }
 
 #[test]
 #[ignore]
 fn multiplication_with_small_operands() {
-    assert_eq!(SimpleCalculator::calculate(3, 21, Option::Some("*")).unwrap(), "3 * 21 = 63");
+    assert_eq!(SimpleCalculator::calculate(3, 21, "*").unwrap(), "3 * 21 = 63");
 }
 
 #[test]
 #[ignore]
 fn multiplication_with_large_operands() {
     assert_eq!(
-        SimpleCalculator::calculate(72_441, 2_048, Option::Some("*")).unwrap(),
-        "72441 * 2048 = 148359168"
+        SimpleCalculator::calculate(72_441, 2_048, "*").unwrap(), "72441 * 2048 = 148359168"
     );
 }
 
 #[test]
 #[ignore]
 fn division_with_small_operands() {
-    assert_eq!(SimpleCalculator::calculate(72, 9, Option::Some("/")).unwrap(), "72 / 9 = 8");
+    assert_eq!(SimpleCalculator::calculate(72, 9, "/").unwrap(), "72 / 9 = 8");
 }
 
 #[test]
 #[ignore]
 fn division_with_large_operands() {
     assert_eq!(
-        SimpleCalculator::calculate(1_338_800, 83_675, Option::Some("/")).unwrap(),
-        "1338800 / 83675 = 16"
+        SimpleCalculator::calculate(1_338_800, 83_675, "/").unwrap(), "1338800 / 83675 = 16"
     );
 }
 
 #[test]
 #[ignore]
 fn calculate_returns_result_err_for_non_valid_operations() {
-    assert_eq!(
-        SimpleCalculator::calculate(1, 2, Option::Some("**")).unwrap_err(),
-        "Operation is out of range"
-    );
-}
-
-#[test]
-#[ignore]
-#[should_panic(expected: ('Operation cannot be null',))]
-fn calculate_panics_for_null_as_operation() {
-    let _ = SimpleCalculator::calculate(1, 2, Option::None);
+    assert_eq!(SimpleCalculator::calculate(1, 2, "**").unwrap_err(), "Operation is out of range");
 }
 
 #[test]
 #[ignore]
+#[should_panic(expected: ("Operation cannot be an empty string",))]
 fn calculate_returns_result_err_for_empty_string_as_operation() {
-    assert_eq!(
-        SimpleCalculator::calculate(1, 2, Option::Some("")).unwrap_err(),
-        "Operation cannot be an empty string"
-    );
+    let _ = SimpleCalculator::calculate(1, 2, "");
 }
 
 #[test]
 #[ignore]
-#[should_panic(expected: ("Division by zero is not allowed",))]
+#[should_panic(expected: ('Division by zero is not allowed',))]
 fn calculate_panics_for_division_with_0() {
-    let _ = SimpleCalculator::calculate(33, 0, Option::Some("/"));
+    let _ = SimpleCalculator::calculate(33, 0, "/");
 }