In this AoPS thread you can find multiple extremely fast ways to calculate \(9+27\). http://www.artofproblemsolving.com/Forum/viewtopic.php?f=224&t=572612
I've used this thread multiple times to prepare for AIME, so I would recommend you guys check it out.
You can post your favorite way to calculate \(9+27\) in the comments below if you want.
Have fun! ^_^