diff --git a/calculator.js b/calculator.js
index caf34db..9368b28 100644
--- a/calculator.js
+++ b/calculator.js
@@ -1,5 +1,5 @@
 function isNumber(numStr){
-  var re = /^[0-9\.]+$/; 
+  var re = /^[0-9\.\-]+$/;
   return re.test(numStr);
 }
 
@@ -11,5 +11,16 @@ function substract(num1, num2){
   return num1 - num2;
 }
 
+function multiplication(num1, num2){
+  return num1 * num2;
+}
+
+function division(num1, num2){
+  return num1 / num2;
+}
+
 module.exports.add = add;
+module.exports.substract = substract;
+module.exports.multiplication = multiplication;
+module.exports.division = division;
 module.exports.isNumber = isNumber;
diff --git a/index.html b/index.html
index cc6a9d9..e5fbd57 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="multiplication">×</option>
+      <option value="division">÷</option>
     </select>
     <input type="text" id="num2" value="1" />
     <div>=</div>
diff --git a/main.js b/main.js
index 957a234..835fc79 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 == "multiplication"){
+      document.getElementById('ans').value = multiplication(num1, num2);
+    }
+    else if (operator == "division"){
+      document.getElementById('ans').value = division(num1, num2);
+    }
     else {
       alert("Bad operator!")
     }
diff --git a/test/test_calculator.js b/test/test_calculator.js
index 13f6205..2a498b3 100644
--- a/test/test_calculator.js
+++ b/test/test_calculator.js
@@ -4,7 +4,21 @@ var cal = require('../calculator.js')
 describe('Calculator', function(){
   describe('add', function(){
     it('add', function(){
-      assert.equal('2', cal.add(1, 1));
+      assert.equal('123', cal.add(54, 69));
+    })
+    it('substract', function(){
+      assert.equal('-12', cal.substract(46, 58));
+    })
+    it('multiplication', function(){
+      assert.equal('1036', cal.multiplication(28, 37));
+    })
+    it('division', function(){
+      assert.equal('91', cal.division(1547, 17));
+    })
+  })
+describe('Unvalid Input', function(){
+    it('not a number', function(){
+      assert.equal(false, cal.isNumber('Hello'))
     })
   })
 })