Nice examples everyone, thanks!

Sean - I can only sell items individually and then in a second, pre-set quantity but that second quantity can differ between products. It could be 15 for Product A but 11 for Product B.

I've designed the table for quantities so that more can be added in the future. Although I don't see that happening, I didn't want to create a flat table design and find out in 6 months it's changing and I'd have to redesign my tables.

Mark