diff --git a/app/libraries/Calculator.php b/app/libraries/Calculator.php
index 3fd2190..26a184e 100644
--- a/app/libraries/Calculator.php
+++ b/app/libraries/Calculator.php
@@ -8,4 +8,29 @@ public function add($x, $y)
     }
     return $x + $y;
   }
+  
+  public function sub($x, $y)
+  {
+      if ( !is_numeric($x) || !is_numeric($y)) {
+          throw new \InvalidArgumentException;
+      }
+      return $x - $y;
+  }
+  
+  public function mul($x, $y)
+  {
+      if ( !is_numeric($x) || !is_numeric($y)) {
+          throw new \InvalidArgumentException;
+      }
+      return $x * $y;
+  }
+  
+  public function div($x, $y)
+  {
+      if ( !is_numeric($x) || !is_numeric($y)) {
+          throw new \InvalidArgumentException;
+      }
+      return $x / $y;
+  }
+  
 }
\ No newline at end of file
diff --git a/test/CalculatorTest.php b/test/CalculatorTest.php
index 6e5dff9..47b787c 100644
--- a/test/CalculatorTest.php
+++ b/test/CalculatorTest.php
@@ -9,7 +9,7 @@ public function setUp()
     $this->calculator = new Calculator;
   }
 
-  public function inputNumbers()
+  public function inputNumbersForSum()
   {
     return [
       [2, 2, 4],
@@ -17,8 +17,32 @@ public function inputNumbers()
     ];
   }
 
+  public function inputNumbersForSubstract()
+  {
+      return [
+          [2, 2, 0],
+          [-20, -5, -15]
+      ];
+  }
+  
+  public function inputNumbersForMultiply()
+  {
+      return [
+        [2, 4, 8],
+        [10, 20, 200]
+      ];
+  }
+
+  public function inputNumbersForDivide()
+  {
+      return [
+        [12, 6, 2],
+        [10, 5, 2]
+      ];
+  }
+
   /**
-   * @dataProvider inputNumbers
+   * @dataProvider inputNumbersForSum
    */
   public function testCanAddNumbers($x, $y, $sum)
   {
@@ -32,5 +56,32 @@ public function testThrowsExceptionIfNonNumberIsPassed()
   {
     $calc = new Calculator;
     $calc->add('a', 'b');
+    $calc->sub('2', 'b');
+    $calc->mul('3', 'c');
+    $calc->div('20', 'a');
+  }
+  
+  /**
+   * @dataProvider inputNumbersForSubstract
+   */
+  public function testCanSubstractNumber($x, $y, $sub)
+  {
+      $this->assertEquals($sub, $this->calculator->sub($x, $y));
+  }
+  
+  /**
+   * @dataProvider inputNumbersForMultiply
+   */
+  public function testCanMultiplyNumbers($x, $y, $mul)
+  {
+      $this->assertEquals($mul, $this->calculator->mul($x, $y));
+  }
+  
+  /**
+   * @dataProvider inputNumbersForDivide
+   */
+  public function testCanDivideNumbers($x, $y, $div)
+  {
+      $this->assertEquals($div, $this->calculator->div($x, $y));
   }
 }
\ No newline at end of file
diff --git a/vendor/autoload.php b/vendor/autoload.php
index d6e96dd..5c33b76 100644
--- a/vendor/autoload.php
+++ b/vendor/autoload.php
@@ -1,7 +1,7 @@
 <?php
 
-// autoload.php generated by Composer
+// autoload.php @generated by Composer
 
 require_once __DIR__ . '/composer' . '/autoload_real.php';
 
-return ComposerAutoloaderInit4cfd9c3a1c44ce88293b671eed43b735::getLoader();
+return ComposerAutoloaderInit2ad21367cd9ccec772a6c779bfd35271::getLoader();
diff --git a/vendor/composer/ClassLoader.php b/vendor/composer/ClassLoader.php
index a4a0dc5..1db8d9a 100644
--- a/vendor/composer/ClassLoader.php
+++ b/vendor/composer/ClassLoader.php
@@ -49,7 +49,7 @@ class ClassLoader
 
     public function getPrefixes()
     {
-        return $this->prefixes;
+        return call_user_func_array('array_merge', $this->prefixes);
     }
 
     public function getFallbackDirs()
@@ -75,28 +75,63 @@ public function addClassMap(array $classMap)
     }
 
     /**
-     * Registers a set of classes
+     * Registers a set of classes, merging with any others previously set.
      *
-     * @param string       $prefix The classes prefix
-     * @param array|string $paths  The location(s) of the classes
+     * @param string       $prefix  The classes prefix
+     * @param array|string $paths   The location(s) of the classes
+     * @param bool         $prepend Prepend the location(s)
      */
-    public function add($prefix, $paths)
+    public function add($prefix, $paths, $prepend = false)
     {
         if (!$prefix) {
-            foreach ((array) $paths as $path) {
-                $this->fallbackDirs[] = $path;
+            if ($prepend) {
+                $this->fallbackDirs = array_merge(
+                    (array) $paths,
+                    $this->fallbackDirs
+                );
+            } else {
+                $this->fallbackDirs = array_merge(
+                    $this->fallbackDirs,
+                    (array) $paths
+                );
             }
 
             return;
         }
-        if (isset($this->prefixes[$prefix])) {
-            $this->prefixes[$prefix] = array_merge(
-                $this->prefixes[$prefix],
-                (array) $paths
+
+        $first = $prefix[0];
+        if (!isset($this->prefixes[$first][$prefix])) {
+            $this->prefixes[$first][$prefix] = (array) $paths;
+
+            return;
+        }
+        if ($prepend) {
+            $this->prefixes[$first][$prefix] = array_merge(
+                (array) $paths,
+                $this->prefixes[$first][$prefix]
             );
         } else {
-            $this->prefixes[$prefix] = (array) $paths;
+            $this->prefixes[$first][$prefix] = array_merge(
+                $this->prefixes[$first][$prefix],
+                (array) $paths
+            );
+        }
+    }
+
+    /**
+     * Registers a set of classes, replacing any others previously set.
+     *
+     * @param string       $prefix The classes prefix
+     * @param array|string $paths  The location(s) of the classes
+     */
+    public function set($prefix, $paths)
+    {
+        if (!$prefix) {
+            $this->fallbackDirs = (array) $paths;
+
+            return;
         }
+        $this->prefixes[substr($prefix, 0, 1)][$prefix] = (array) $paths;
     }
 
     /**
@@ -142,7 +177,7 @@ public function unregister()
      * Loads the given class or interface.
      *
      * @param  string    $class The name of the class
-     * @return bool|null True, if loaded
+     * @return bool|null True if loaded, null otherwise
      */
     public function loadClass($class)
     {
@@ -158,10 +193,11 @@ public function loadClass($class)
      *
      * @param string $class The name of the class
      *
-     * @return string|null The path, if found
+     * @return string|false The path if found, false otherwise
      */
     public function findFile($class)
     {
+        // work around for PHP 5.3.0 - 5.3.2 https://bugs.php.net/50731
         if ('\\' == $class[0]) {
             $class = substr($class, 1);
         }
@@ -172,7 +208,7 @@ public function findFile($class)
 
         if (false !== $pos = strrpos($class, '\\')) {
             // namespaced class name
-            $classPath = str_replace('\\', DIRECTORY_SEPARATOR, substr($class, 0, $pos)) . DIRECTORY_SEPARATOR;
+            $classPath = strtr(substr($class, 0, $pos), '\\', DIRECTORY_SEPARATOR) . DIRECTORY_SEPARATOR;
             $className = substr($class, $pos + 1);
         } else {
             // PEAR-like class name
@@ -180,13 +216,16 @@ public function findFile($class)
             $className = $class;
         }
 
-        $classPath .= str_replace('_', DIRECTORY_SEPARATOR, $className) . '.php';
+        $classPath .= strtr($className, '_', DIRECTORY_SEPARATOR) . '.php';
 
-        foreach ($this->prefixes as $prefix => $dirs) {
-            if (0 === strpos($class, $prefix)) {
-                foreach ($dirs as $dir) {
-                    if (file_exists($dir . DIRECTORY_SEPARATOR . $classPath)) {
-                        return $dir . DIRECTORY_SEPARATOR . $classPath;
+        $first = $class[0];
+        if (isset($this->prefixes[$first])) {
+            foreach ($this->prefixes[$first] as $prefix => $dirs) {
+                if (0 === strpos($class, $prefix)) {
+                    foreach ($dirs as $dir) {
+                        if (file_exists($dir . DIRECTORY_SEPARATOR . $classPath)) {
+                            return $dir . DIRECTORY_SEPARATOR . $classPath;
+                        }
                     }
                 }
             }
diff --git a/vendor/composer/autoload_classmap.php b/vendor/composer/autoload_classmap.php
index 4e01093..f4a2678 100644
--- a/vendor/composer/autoload_classmap.php
+++ b/vendor/composer/autoload_classmap.php
@@ -1,8 +1,8 @@
 <?php
 
-// autoload_classmap.php generated by Composer
+// autoload_classmap.php @generated by Composer
 
-$vendorDir = dirname(__DIR__);
+$vendorDir = dirname(dirname(__FILE__));
 $baseDir = dirname($vendorDir);
 
 return array(
diff --git a/vendor/composer/autoload_namespaces.php b/vendor/composer/autoload_namespaces.php
index 43b324a..b7fc012 100644
--- a/vendor/composer/autoload_namespaces.php
+++ b/vendor/composer/autoload_namespaces.php
@@ -1,8 +1,8 @@
 <?php
 
-// autoload_namespaces.php generated by Composer
+// autoload_namespaces.php @generated by Composer
 
-$vendorDir = dirname(__DIR__);
+$vendorDir = dirname(dirname(__FILE__));
 $baseDir = dirname($vendorDir);
 
 return array(
diff --git a/vendor/composer/autoload_real.php b/vendor/composer/autoload_real.php
index 6436674..9d730c2 100644
--- a/vendor/composer/autoload_real.php
+++ b/vendor/composer/autoload_real.php
@@ -1,8 +1,8 @@
 <?php
 
-// autoload_real.php generated by Composer
+// autoload_real.php @generated by Composer
 
-class ComposerAutoloaderInit4cfd9c3a1c44ce88293b671eed43b735
+class ComposerAutoloaderInit2ad21367cd9ccec772a6c779bfd35271
 {
     private static $loader;
 
@@ -15,20 +15,20 @@ public static function loadClassLoader($class)
 
     public static function getLoader()
     {
-        if (null !== static::$loader) {
-            return static::$loader;
+        if (null !== self::$loader) {
+            return self::$loader;
         }
 
-        spl_autoload_register(array('ComposerAutoloaderInit4cfd9c3a1c44ce88293b671eed43b735', 'loadClassLoader'));
-        static::$loader = $loader = new \Composer\Autoload\ClassLoader();
-        spl_autoload_unregister(array('ComposerAutoloaderInit4cfd9c3a1c44ce88293b671eed43b735', 'loadClassLoader'));
+        spl_autoload_register(array('ComposerAutoloaderInit2ad21367cd9ccec772a6c779bfd35271', 'loadClassLoader'), true, true);
+        self::$loader = $loader = new \Composer\Autoload\ClassLoader();
+        spl_autoload_unregister(array('ComposerAutoloaderInit2ad21367cd9ccec772a6c779bfd35271', 'loadClassLoader'));
 
         $vendorDir = dirname(__DIR__);
         $baseDir = dirname($vendorDir);
 
         $map = require __DIR__ . '/autoload_namespaces.php';
         foreach ($map as $namespace => $path) {
-            $loader->add($namespace, $path);
+            $loader->set($namespace, $path);
         }
 
         $classMap = require __DIR__ . '/autoload_classmap.php';
@@ -36,7 +36,7 @@ public static function getLoader()
             $loader->addClassMap($classMap);
         }
 
-        $loader->register();
+        $loader->register(true);
 
         return $loader;
     }