Get out your timer and number two pencil to see if your arithmetic skills from grade school are still intact.

Add Yahoo as a preferred source to see more of our stories on Google. We like to think that we're pretty good at math, especially after years of schooling. But every once in a while, a simple ...

On paper, it’s one of the simplest math problems in the world: 2+2. If you’re counting something, like screws at the hardware store, it’s pretty straightforward. But the lines blur in other contexts.