单选题 A certain brand of house paint must be purchased either in quarts at $12 each or in gallons at $18 each.A painter needs a 3-gallon mixture of the paint consisting of 3 parts blue and 2 parts white.What is the least amount of money needed to purchase sufficient quantities of the two colors to make the mixture? (4 quarts=1 gallon)
【正确答案】 C
【答案解析】To make 3 gallons of the mixture requires 12 quarts, and the least amount of money is achieved by purchasing the greatest number of gallons and least number of quarts. Letting B be the number of quarts of blue paint needed and W be the number of quarts of white paint needed, it follows that B + W= 12, where B = 3W/2 since the mixture has a blue to white ratio of 3 to 2. This gives B= and W=