How many brownies does a box of mix make?

It is usually around 6 and sometimes 12.

Depends what you bought, the no.of servings will be given at the back side of the box. And if this recipe is online generally they give the no.of servings that can be made with those amounts of ingredients but if its not given, to be on the safe side use exact half of all the ingredients mentioned or use only half of the mix given.

Hope it helped! :)