Robin invested a total of $12,000 in two investments, X and Y, so that the investments earned the same amount of simple annual interest. How many dollars did Robin invest in investment Y? Investment X paid 3 percent simple annual interest, and investment Y paid 6 percent simple annual interest.

x = $8000, y = $4000

Explanation:

Simple interest = (Principal x Rate x Time) / 100,

where P is principal,

R rate of interest and

T is time

The scenario states that the two rate of interest are 3% and 6%

Therefore

So X*3*1 / 100=Y*6*1/100.

or if we are to substitute x values for y

So X*3*1 / 100 = (12000-X) * 6*1/100

0.03x = 720 - 0.06x

0.09x = 720

x = $8000

and Y = 12000 - x which is 12000 - 8000 = $4000

To check

3% of 8000 = 240

6% of 4000 = 240