Question 615830
Let us say that the amount invested at 8% is a.

A percentage simply represents how many units out of 100 so 8% can be written as 8/100 or 0.08 and 12% can therefore be written as 12/100 or 0.12

so if 'a' is the amount invested at 8% then the amount invested at 12% is:
2a + 2000
(twice 'a' plus 2000)


The gain is the percent of that investment (I assume that it is on the original investment, not accrued).

So the amount returned from the 8% investment is simply 0.08a

The amount returned from the 12% investment is 0.12(2a + 2000)

which can then be simplified by multiplying 0.12 by each part of the formula within the brackets:

(0.12 x 2a) + (0.12 x 2000) = 0.24a + 240

So the total return is that money that comes from both investments:
  = 0.08a + 0.24a + 240
  = 0.32a + 240

As we know the amount of the return is $4720 (I assume it represents the interest income)

So:

0.32a + 240 = 4720
0.32a = 4720 - 240
0.32a = 4480
so  a = 4480/0.32
    a = 14000


So now we know 'a' we can figure out the amount invested at 12 % which is
2a + 2000

So:

2a + 2000 = 2*14000 + 2000
          = 28000 + 2000
          = 30000

The amount invested at 12% is $30000