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?
3/8 of the mixture is white; 5/8 is black. Then for 2 gallons of mixture, .. (3/8)*2 gal = 3/4 gal of white paint are needed, and .. (5/8)*2 gal = 5/4 gal of black paint are needed. Rounding up to the nearest 1/2 gallon, .. 1 gallon of white and 1 1/2 gallons of black must be purchased, for a total of 2 1/2 gallons of paint.
