Question

i hate story problems

Answer 1

well if you have 7200 and invest x at 10% and that leaves 7200 -x at 9%


then 0.1x + -.09(7200 - x) = 680

expand, collect like terms and then solve for x

Answer 2

Interest of 10% + Interest of 9% = total Interest
P R t + p r t = $680
As Campell's logic above:
t = 1 year, x is 10% principal, then:
10% x + 9% ( 7,200 - x) = $680
-> 10% x - 9%x = 680 - 648
=> .01 x = 32
=> x = $3,200 principal portion on 10%