diff --git a/08_calculator/calculator.js b/08_calculator/calculator.js
index a89ce8c..28a6476 100644
--- a/08_calculator/calculator.js
+++ b/08_calculator/calculator.js
@@ -6,8 +6,11 @@ const subtract = function(a, b) {
 	return a - b;
 };
 
-const sum = function() {
-	
+const sum = function(array) {
+	const output = array.reduce((total, value) => {
+    return total + value;
+  }, 0);
+  return output;
 };
 
 const multiply = function() {
diff --git a/08_calculator/calculator.spec.js b/08_calculator/calculator.spec.js
index 996f4c9..33e9367 100644
--- a/08_calculator/calculator.spec.js
+++ b/08_calculator/calculator.spec.js
@@ -21,19 +21,19 @@ describe('subtract', () => {
 });
 
 describe('sum', () => {
-  test.skip('computes the sum of an empty array', () => {
+  test('computes the sum of an empty array', () => {
     expect(calculator.sum([])).toBe(0);
   });
 
-  test.skip('computes the sum of an array of one number', () => {
+  test('computes the sum of an array of one number', () => {
     expect(calculator.sum([7])).toBe(7);
   });
 
-  test.skip('computes the sum of an array of two numbers', () => {
+  test('computes the sum of an array of two numbers', () => {
     expect(calculator.sum([7, 11])).toBe(18);
   });
 
-  test.skip('computes the sum of an array of many numbers', () => {
+  test('computes the sum of an array of many numbers', () => {
     expect(calculator.sum([1, 3, 5, 7, 9])).toBe(25);
   });
 });