单选题
A certain shade of gray paint is obtained by mixing 3 parts of white paint with 5 parts of black paint. If 2 gallons of the mixture is needed and the individual colors can be purchased only in one-gallon or half gallon cans, what is the least amount of paint, in gallons, that must be purchased in order to measure out the portions needed for the mixture?
【正确答案】
B
【答案解析】[解析] 根据题意可设需要白色颜料3x加仑，需要黑色颜料为5x加仑来配出2加仑的混合颜料：
3x+5x=2→x=0.25加仑，因此需要0.75加仑的白色颜料和1.25加仑的黑色颜料，而这些颜料只能以1加仑一筒或0.5加仑一筒的形式购买，所以需要买1加仑白色颜料和1.5加仑的黑色颜料，共2.5加仑。
3x+5x=2→x=0.25加仑，因此需要0.75加仑的白色颜料和1.25加仑的黑色颜料，而这些颜料只能以1加仑一筒或0.5加仑一筒的形式购买，所以需要买1加仑白色颜料和1.5加仑的黑色颜料，共2.5加仑。