Given that all bevels are dowels, where there are 12 bevels and 20 dowels, it means there are 12 bevels that are dowels and 8 dowels that are not bevels.
Furthermore, if all dowels are swivels, and there are 30 swivels then the number of swivels that are neither bevels nor dowels
= 30 - 20
= 10
There are 10 swivels that are not bevels or dowels.
