Why is Twitter Bootstrap Grid System with 12 columns instead of 10 (let's say 100%)?

Question

If 10 can represent 100% (on CSS width for example) why is this grid system for 12 columns instead of only 10? I guess other frameworks have it also that way.

Answer 1

12 can be divided evenly by 2, 3, 4 and 6, so you can easily make 2, 3, and 4 column layouts with the same grid. That's not nice to do with a grid of 10 columns.