diff --git a/calculator.py b/calculator.py
index a46affd..30c2107 100644
--- a/calculator.py
+++ b/calculator.py
@@ -40,45 +40,111 @@
 
 
 """
+import traceback
+from numpy import prod
 
 
 def add(*args):
     """ Returns a STRING with the sum of the arguments """
+    return sum(map(int, args))
+
+
+def subtract(*args):
+    """ Returns a STRING, in which the first number retains its value, the remaining numbers
+    take their negative value, and all numbers are summed."""
+    args_mut = []
+    for i in range(len(args)):
+        args_mut.append('')
+        if i == 0:
+            args_mut[i] = int(args[i])
+        else:
+            args_mut[i] = int(args[i]) * -1
+    return sum(map(int, args_mut))
+
+
+def multiply(*args):
+    """ Returns a STRING, in which all numbers are multiplied in sequence."""
+    return prod(list(map(int, args)))
+
+
+def divide(*args):
+    """ Returns a STRING, in which the numbers are divided in sequence.
+    ZeroDivisionError included."""
+    if '0' in args[1:]:
+        raise ZeroDivisionError
+
+    args_mut = []
+    for arg in args:
+        args_mut.append(int(arg))
+    quotient = args_mut[0]
+    for i in range(1, len(args_mut)):
+        quotient /= args_mut[i]
+
+    return quotient
+
+
+def instructions():
+    """Return an html string of instructions."""
+    page = """
+<h1>Instructions</h1>
+<ul>
+<li>add, subtract, multiply, or divide goes after root</li>
+<li>any sequence of integers separated by / goes next</li>
+<li>example: http://127.0.0.1:8080/divide/2/5/9/10</li>
+</ul>
+"""
 
-    # TODO: Fill sum with the correct value, based on the
-    # args provided.
-    sum = "0"
-
-    return sum
+    return page
 
-# TODO: Add functions for handling more arithmetic operations.
 
 def resolve_path(path):
     """
     Should return two values: a callable and an iterable of
     arguments.
     """
+    funcs = {'': instructions, 'add': add, 'subtract': subtract, 'multiply': multiply,
+             'divide': divide}
+
+    path = path.strip('/').split('/')
 
-    # TODO: Provide correct values for func and args. The
-    # examples provide the correct *syntax*, but you should
-    # determine the actual values of func and args using the
-    # path.
-    func = add
-    args = ['25', '32']
+    func_name = path[0]
+    args = path[1:]
+
+    try:
+        func = funcs[func_name]
+    except KeyError:
+        raise NameError
 
     return func, args
 
+
 def application(environ, start_response):
-    # TODO: Your application code from the book database
-    # work here as well! Remember that your application must
-    # invoke start_response(status, headers) and also return
-    # the body of the response in BYTE encoding.
-    #
-    # TODO (bonus): Add error handling for a user attempting
-    # to divide by zero.
-    pass
+    """Provide the response, including for raised ZeroDivisionError."""
+    headers = [('Content-type', 'text/html')]
+    try:
+        path = environ.get('PATH_INFO', None)
+        if path is None:
+            raise NameError
+        func, args = resolve_path(path)
+        body = func(*args)
+        status = "200 OK"
+    except NameError:
+        status = "404 Not Found"
+        body = "<h1> Not Found</h1>"
+    except ZeroDivisionError:
+        status = "403 Forbidden"
+        body = "<h1>Division by Zero Not Permitted</h1>"
+    except Exception:
+        status = "500 Internal Server Error"
+        body = "<h1>Internal Server Error</h1>"
+        print(traceback.format_exc())
+    finally:
+        headers.append(('Content-length', str(len(str(body)))))
+        start_response(status, headers)
+    return [str(body).encode('utf8')]
+
 
 if __name__ == '__main__':
-    # TODO: Insert the same boilerplate wsgiref simple
-    # server creation that you used in the book database.
-    pass
+    from wsgiref.simple_server import make_server
+    srv = make_server('127.0.0.1', 8080, application)
+    srv.serve_forever()
diff --git a/tests.py b/tests.py
index c2a8dcb..7a91ed5 100644
--- a/tests.py
+++ b/tests.py
@@ -26,7 +26,7 @@ def get_response(self, url):
         Helper function to get a response from a given url, using http.client
         """
 
-        conn = http.client.HTTPConnection('localhost:8080')
+        conn = http.client.HTTPConnection('127.0.0.1:8080')
         conn.request('GET', url)
 
         response = conn.getresponse()