As an alternate answer, you could possibly use the built-in graphic repository manager.
Do this by:
Open the Ubuntu Software Center:
Do this by clicking on the link on your Launcher.
Or, if you have removed it from the launcher, you can search for it via the dash.
Open the Software Sources menu:
Do this by locating the Edit menu and selecting 'Software Sources...'
then once the window has opened, move to the 'Other Sources' tab.
Add the PPA via the window:
Below your list of current PPAs, click the 'Add' button.
And when the window appears, enter the PPA address, which in your case is deb http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu precise main and deb-src http://ppa.launchpad.net/ubuntu-toolchain-r/test/ubuntu precise main
And click 'Add Source'.
You may also need to provide authentication by entering your user password.
And that's it.
Even if this doesn't work, the Software Centre may come up with a window with an error message, and most likely how to fix it. You won't believe what I went through to find a solution through the command-line and failed, and how relieved I was when I used the GUI and Ubuntu just spat the words out without me having to do anything. You may also want to combine these steps with the answer above, regarding the spelling error and such.
Cheers and good luck!