这题我明明见有人问过，答案是2.5啊。 A certain shade of gray paint is obtained by mixing 3 parts of white paint with 5parts of black paint. 可知道得到一份gray paint ，需要3/8份white paint ， 5/8份black paint If 2 gallons of the mixture is needed 可知道得到2 gallons gray paint ，需要3/4gallon white paint ， 5/4 gallons black paint the individual colors can be purchased only in one gallon or half galloncans,what is the least amount of paint ,in gallons, 所以需要1 gallon white paint ， 1.5 gallon black paint，共2.5 | 
