Yay for Sass! 

Returns after commas, and added spaces after each selector. (it's Sass, let them breath since they're going to get compiled anyway)
```scss
$gallery-slug: gallery-columns !default;

@for $i from 2 through 9 {
  .#{$gallery-slug}-#{$i} {
    max-width: #{100 / $i}%;
  }
}
```
Only 7 lines of code instead of 30!