Marsha invested part of $18,000 at 16% simple annual interest and the remaining at 20% simple annual interest her total yearly income from investments was $3,120 how much was invested at each rate

Answer 1

.20x + .16(18,000-x) = 3,120

.20x- .16x = 3120 -.16(18000)

.04x = 3120-2880 = 240

x=240/.04 = $6,000 invested at 20%

18000-6000 = $12,000 invested at 16%

.2(6) +.16(12) = 1.2 +1.92 = 3.12 thousand dollars

3120/18,000= 17.333...% return on both investments

.20 is within 2 2/3 of 17 1/3

16 is within 1 1/3 of 17 1/3

2 2/3 is twice 1 1/3 so you need twice as much invested at16%

12,000 is twice 6,000