Arman has 1160 annual income from bonds bearing 3% and 5 % interest. then he added 25% more of the 3% bonds and 40% more of the 5 % bonds, thereby increasing his annual income by 410. find his initial investment in each type of bond

Question

(if you would,just give me the formula and i'll take it from there)

thank you

Answer 1

I will do it using two variables

let the original 3% investment be x
let the original 5% investment by y

.03x + .05y = 1160 or 3x + 5y = 116000

after stated increase in each investment:
.03(1.25x) + .05(1.4y) = 1570
or after multiplying by 100
3.75x +7y = 157000
times 4
15x + 28y = 628000

you now have 2 equations in 2 unknowns, take it from there. (y=16000 , x = 12000)