Answer:
$4000
Step-by-step explanation:
Assuming a = money invested at 9%
Assuming b = money invested at 8%
then we can form am equation from the question given
1) a + b = $10000, also
0.09a + 0.08b = $860 -> multiply by 100
2) 9a + 8b = $86000
Next we try to solve both equations simultaneously. We multiply both the left hand side and the right hand side of the first equation by 8. We have
3) 8a + 8b = $80000, now we subtract 3 from 2
9a + 8b = $86000
-8a - 8b = -$80000
a = $6000.
Then, we plug this in any of the first 2 equations, to get b
9 * $6000 + 8b = $86000
$54000 + 8b = $86000
8b = $86000 - $54000
8b = $32000
b = $32000/8
b = $4000.
Therefore, he invested $4000 at 8%
