diff --git a/08_calculator/calculator.js b/08_calculator/calculator.js
index c22e8d2..8b23122 100644
--- a/08_calculator/calculator.js
+++ b/08_calculator/calculator.js
@@ -1,25 +1,34 @@
-const add = function() {
-	
+const add = function(n , m) {
+  return n + m;
 };
 
-const subtract = function() {
-	
+const subtract = function(n , m) {
+	return n - m;
 };
 
-const sum = function() {
-	
+const sum = function(myArray) {
+	let s = 0;
+  for(let i = 0 ;i < myArray.length ; i++){
+    s += myArray[i];
+  }
+  return s;
 };
 
-const multiply = function() {
-
+const multiply = function(myArray) {
+  let m = 1;
+  for(let i = 0 ;i < myArray.length ; i++){
+    m *= myArray[i];
+  }
+  return m;
 };
 
-const power = function() {
-	
+const power = function(n , m) {
+	return Math.pow(n , m);
 };
 
-const factorial = function() {
-	
+const factorial = function(n) {
+	if(n < 2) return 1;
+  return n * factorial(n - 1);
 };
 
 // Do not edit below this line
diff --git a/08_calculator/calculator.spec.js b/08_calculator/calculator.spec.js
index 48b08c9..59956fe 100644
--- a/08_calculator/calculator.spec.js
+++ b/08_calculator/calculator.spec.js
@@ -5,73 +5,73 @@ describe('add', () => {
     expect(calculator.add(0, 0)).toBe(0);
   });
 
-  test.skip('adds 2 and 2', () => {
+  test('adds 2 and 2', () => {
     expect(calculator.add(2, 2)).toBe(4);
   });
 
-  test.skip('adds positive numbers', () => {
+  test('adds positive numbers', () => {
     expect(calculator.add(2, 6)).toBe(8);
   });
 });
 
 describe('subtract', () => {
-  test.skip('subtracts numbers', () => {
+  test('subtracts numbers', () => {
     expect(calculator.subtract(10, 4)).toBe(6);
   });
 });
 
 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);
   });
 });
 
 describe('multiply', () => {
-  test.skip('multiplies two numbers', () => {
+  test('multiplies two numbers', () => {
     expect(calculator.multiply([2, 4])).toBe(8);
   });
 
-  test.skip('multiplies several numbers', () => {
+  test('multiplies several numbers', () => {
     expect(calculator.multiply([2, 4, 6, 8, 10, 12, 14])).toBe(645120);
   });
 });
 
 describe('power', () => {
-  test.skip('raises one number to the power of another number', () => {
+  test('raises one number to the power of another number', () => {
     expect(calculator.power(4, 3)).toBe(64); // 4 to third power is 64
   });
 });
 
 describe('factorial', () => {
-  test.skip('computes the factorial of 0', () => {
+  test('computes the factorial of 0', () => {
     expect(calculator.factorial(0)).toBe(1); // 0! = 1
   });
 
-  test.skip('computes the factorial of 1', () => {
+  test('computes the factorial of 1', () => {
     expect(calculator.factorial(1)).toBe(1);
   });
 
-  test.skip('computes the factorial of 2', () => {
+  test('computes the factorial of 2', () => {
     expect(calculator.factorial(2)).toBe(2);
   });
 
-  test.skip('computes the factorial of 5', () => {
+  test('computes the factorial of 5', () => {
     expect(calculator.factorial(5)).toBe(120);
   });
 
-  test.skip('computes the factorial of 10', () => {
+  test('computes the factorial of 10', () => {
     expect(calculator.factorial(10)).toBe(3628800);
   });
 });