Just for the benefit of you and the searchers, the Additional Drivers tool happily and cheerfully installs the wrong driver in several cases. Please check the sticky and compare your pci.id. If yours requires something other than bcmwl-kernel-source, then you will need to remove the incorrect driver, as outlined in the sticky, install the correct driver or, more likely, firmware and then reboot.
The pci.id is everything; it is needed to identify the device and thereafter install the correct driver or firmware. Searchers, do not just read any old BT4 or Arch or Suse thread and read that for some obscure Broadcom that is undoubtedly not the same as yours; that you need to boil a skunk in kerosene and chant a magic incantation to get your Broadcom working. It probably won't work and you'll end up with a big mess that Iowan and mörgæs and I will spend hours undoing.
Please do not bring me your boiled skunk.
"Oh, Ubuntu, you are my favorite Linux-based operating system" --Dr. Sheldon Cooper, Ph.D.