A man invests his savings in two accounts, one paying 6% and the other paying 10% simple interest per year. He puts twice as much in the lower-yielding account because it is less risky. His annual interest is $2,640. How much did he invest at each rate?
Amount of income at 10% = .10 (x)
Amount of income at 6% = .06(2x) summed = 2640
.1x + .12x = 2640 solve for x the 10% amount then 6% amount = 2x