OG详解-OG9 数学1 Q25

Choice D is correct. It’s given that w represents the total fence area, in square feet. Since the fence will be stained twice, the amount of stain, in gallons, will need to cover 2w square feet. It’s also given that one gallon of stain will cover 170 square feet. Dividing the total area, in square feet, of the surface to be stained by the number of square feet covered by one gallon of stain gives the number of gallons of stain that will be needed. Dividing 2w by 170 yields2w170​​, or  w85​​. Therefore, the equation that represents the total amount of stain S, in gallons, needed to stain the fence of the yard twice is S =w85​​ .
Choice A is incorrect. This equation represents the total amount of stain, in gallons, needed to stain the fence once, not twice. Choice B is incorrect and may result from conceptual or calculation errors. Choice C is incorrect and may result from conceptual or calculation errors.