How much did she invest at each rate?

Question

Jolene invests her savings in two bank accounts, one paying 4 percent and the other paying 11 percent simple interest per year. She puts twice as much in the lower-yielding account because it is less risky. Her annual interest is 3078 dollars. How much did she invest at each rate? 

Answer 1

.11(x) + .04(2x) = 3078

.11x + .08x = 3078

.19x = 3078

x = 3078/.19

x = = $16,200 invested at 11% and $32,400 invested at 4%

3078/(16200+32400) = 3078/48600 = 6 1/3 %

11 is with 4 2/3 of 6 1/3

4 is within 2 1/3 of 6 1/3

4 2/3 is twice 2 1/3

32400 is twice 16200

You need twice as much invested at the % that's twice as close to the net percentage of the total invested

.11(16200) + .04(32400) = 1782 + 1296 = 3078