Question

A developer wants to develop a 25-acre subdivision. He figures that the streets and common area will take up about 35% of this overall area. If the minimum lot size is to be 25,000 SF, how many lots can the developer have on this property? 15 lots? 65 lots? 28 lots? 34 lots?

Answer 1

The amount avaliable for division into lots is
  25 ac - 0.35*25 ac = 0.65*25 ac = 16.25 ac
There are 43,560 ft² in an acre, so the number of possible lots is
  (16.25 ac)*(43,560 ft²/ac)/(25,000 ft²/lot) = 28.314 lots

The developer has enough area for 28 lots.