Gina plans to invest $12,000, part at 4% simple interest and the rest at 6% simple interest. What is the most she can invest at 4% and still be guranteed at least $650 in interest per year?

Answer 1

x at 4%
(12,000 -x) at 6%
then
.04 x + .06(12000-x) = 650
-.02 x + 720 = 650
.02 x = 70
x = 3500