diff --git a/calculator.js b/calculator.js
index caf34db..c0c858d 100644
--- a/calculator.js
+++ b/calculator.js
@@ -1,5 +1,5 @@
 function isNumber(numStr){
-  var re = /^[0-9\.]+$/; 
+  var re = /^[\-]?[0-9]+[\.]?[0-9]*$/;
   return re.test(numStr);
 }
 
@@ -7,9 +7,18 @@ function add(num1, num2){
   return num1 + num2;
 }
 
+function multiply(num1, num2){
+  return num1 * num2;
+}
+function divide(num1, num2){
+  return num1 / num2;
+}
 function substract(num1, num2){
   return num1 - num2;
 }
 
 module.exports.add = add;
+module.exports.divide = divide;
+module.exports.multiply = multiply;
+module.exports.substract = substract;
 module.exports.isNumber = isNumber;
diff --git a/index.html b/index.html
index cc6a9d9..7951bd0 100644
--- a/index.html
+++ b/index.html
@@ -22,6 +22,8 @@ <h1>Silly Calculator</h1>
     <select id="operator" size="1">
       <option value="add">+</option>
       <option value="substract">-</option>
+      <option value="multiply">*</option>
+      <option value="divide">/</option>
     </select>
     <input type="text" id="num2" value="1" />
     <div>=</div>
diff --git a/main.js b/main.js
index 957a234..b4eebc6 100644
--- a/main.js
+++ b/main.js
@@ -16,6 +16,12 @@ window.onload = function(){
     else if (operator == "substract"){
       document.getElementById('ans').value = substract(num1, num2);
     }
+    else if (operator == "multiply"){
+      document.getElementById('ans').value = multiply(num1, num2);
+    }
+    else if (operator == "divide"){
+      document.getElementById('ans').value = divide(num1, num2);
+    }
     else {
       alert("Bad operator!")
     }
diff --git a/test/test_calculator.js b/test/test_calculator.js
index 13f6205..7fff3fa 100644
--- a/test/test_calculator.js
+++ b/test/test_calculator.js
@@ -2,9 +2,25 @@ var assert = require('assert');
 var cal = require('../calculator.js')
 
 describe('Calculator', function(){
-  describe('add', function(){
+  describe('All Operator', function(){
     it('add', function(){
       assert.equal('2', cal.add(1, 1));
     })
+    it('substract', function(){
+      assert.equal('0', cal.substract(1, 1));
+    })
+    it('multiply', function(){
+      assert.equal('4', cal.multiply(2, 2));
+    })
+    it('divide', function(){
+      assert.equal('2', cal.divide(2, 1));
+    })
   })
+  
+  describe('isnumber', function(){
+  	it('isNumber', function(){
+	      assert.equal(false, cal.isNumber('a'));
+	      assert.equal(true, cal.isNumber(1));
+   	})
+     })
 })