The total capacity of the 40 chairs was 40*2=<<40*2=80>>80 people.
If 2/5 of the chairs were unoccupied, 2/5*80=<<2/5*80=32>>32 people missed the board meeting since the number of members was the same as the chair's capacity.
The number of board members who attended the meeting was 80-32=<<80-32=48>>48
#### 48