diff --git a/08_calculator/calculator.js b/08_calculator/calculator.js
index c22e8d2..298a9f4 100644
--- a/08_calculator/calculator.js
+++ b/08_calculator/calculator.js
@@ -1,17 +1,29 @@
-const add = function() {
-	
+const add = function(a, b) {
+	return a + b;
 };
 
-const subtract = function() {
-	
+const subtract = function(a, b) {
+	return a - b;
 };
 
-const sum = function() {
-	
+const sum = function(array) {
+	let sumArray = 0;
+  if (array.length == 0) {
+    return 0;
+  } else {
+  for (let i = 0; i < array.length; i++) {
+    sumArray += array[i];
+  }
+  return sumArray;
+}
 };
 
-const multiply = function() {
-
+const multiply = function(numbers) {
+  let multiplyNum = 1;
+  for (let i = 0; i < numbers.length; i++) {
+    multiplyNum *= numbers[i];
+  }
+  return multiplyNum;
 };
 
 const power = function() {
diff --git a/08_calculator/calculator.spec.js b/08_calculator/calculator.spec.js
index dc317ec..f617e63 100644
--- a/08_calculator/calculator.spec.js
+++ b/08_calculator/calculator.spec.js
@@ -5,45 +5,45 @@ 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);
 	});
 });