Quick tip –
I often find myself needing to make a quick calculation, but not wanting to whip out a calculator, or dig through menus or folders until I find my built-in calculator (in /Applications on a Mac, in Start->Programs->Accessories on a PC).
Since I almost always have a web page open, I’ve resorted to just using Google.
In the Google search field, or the Google search bar if you have one, or even just in the address bar if you’re using Google’s Chrome browser, type in the math problem. The first item on the list that comes back is your answer:
It does conversions too. Here’s one for temperature: