diff --git a/calculator/calculator.js b/calculator/calculator.js
index 2d904a8..c375891 100644
--- a/calculator/calculator.js
+++ b/calculator/calculator.js
@@ -1,25 +1,33 @@
-function add () {
+function add (a,b) {
+	return a+b;
+}
+
+function subtract (a,b) {
+	return a-b;
+}
+
+function sum (array) {
+	return array.reduce(total,current )=> total+=current,0);
 	
 }
 
-function subtract () {
+function multiply (a,b) {
+	return array.length? array.reduce(accumaltor,nextitem )=> accumaltor*nextitem):0;
+}
+
+function power(a,b) {
+	return Math.pow(a,b)
 	
 }
 
-function sum () {
-	
-}
-
-function multiply () {
-	
-}
-
-function power() {
-	
-}
-
-function factorial() {
-	
+function factorial(a) {
+	if(a==o)return;
+	let fact=1;
+	for(let i=n ;i<0 ;i--)
+	{ 
+	  fact*=1;
+	}
+	return fact;
 }
 
 module.exports = {
@@ -29,4 +37,4 @@ module.exports = {
 	multiply,
     power,
 	factorial
-}
\ No newline at end of file
+}