diff --git a/calculator.js b/calculator.js
index caf34db..d6f35a1 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);
 }
 
@@ -11,5 +11,15 @@ function substract(num1, num2){
   return num1 - num2;
 }
 
+function multiply(num1 ,num2){
+  return num1*num2;
+}
+
+function divide(num1 , num2){
+  return num1/num2;
+}
 module.exports.add = add;
+module.exports.substract = substract;
+module.exports.multiply = multiply;
+module.exports.divide = divide;
 module.exports.isNumber = isNumber;
diff --git a/index.html b/index.html
index cc6a9d9..1f2db54 100644
--- a/index.html
+++ b/index.html
@@ -22,7 +22,9 @@ <h1>Silly Calculator</h1>
     <select id="operator" size="1">
       <option value="add">+</option>
       <option value="substract">-</option>
-    </select>
+	  <option value="multiply">*<option>
+	  <option value="divide">/<option>
+	</select>
     <input type="text" id="num2" value="1" />
     <div>=</div>
     <input type="text" id="ans" value="2" />
diff --git a/main.js b/main.js
index 957a234..f119043 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..965c8ca 100644
--- a/test/test_calculator.js
+++ b/test/test_calculator.js
@@ -4,7 +4,28 @@ var cal = require('../calculator.js')
 describe('Calculator', function(){
   describe('add', function(){
     it('add', function(){
-      assert.equal('2', cal.add(1, 1));
+      assert.equal('8', cal.add(3, 5));
+    })
+  })
+  describe('substract',function(){
+	it('substract',function(){
+		assert.equal('1',cal.substract(2,1));
+	})
+  })
+  describe('multiply',function(){
+	it('multiply',function(){
+		assert.equal('15',cal.multiply(3,5));
+	})
+  })
+  describe('divide', function(){
+    it('divide', function(){
+      assert.equal('5', cal.divide(15, 3));
+    })
+  })
+  describe('isNumber', function(){
+    it('isNumber', function(){
+      assert.equal('1', cal.isNumber(-1));
+      assert.equal('0', cal.isNumber('ABC'));
     })
   })
 })