I had asked this question on Facebook.
Imagine a cube. Put it on a flat surface, so that four vertices are at the bottom and four vertices are on top. Select any vertex on top, and connect it to each of the four vertices at the bottom. This now encloses a part of the cube. Cut this enclosed part off, and you are left with another shape.
How many faces does this leftover shape have?
I feel the answer is seven, but my friends say five. This may be a relatively easy question for this site, but I found it quite hard to visualize.