Centering a grid of images only using CSS

Hi all,

Here is my blogpost on an interview question I ask regularly. I would be grateful if people can give this a read through to check if I'm being clear enough or whether I'm talking about a irrelevant 'problem' which has a well-known solution to save me from looking like a complete plonker.

Also I could probably do with a new title.

A
Summarizing the problem with an image is very useful here. Well done. The imgs seem broken, though but probably just within the context of this review?