Question 726416
A man has two investments totalling $10,000. On one he receives 8% interest and on the other he receives 4% interest. The 8% investment yields an annual income of $320 more than the 4% investment. How much has he invested at each rate?

let one investment be x@8%
and the other be y be @4%

x+y=10000..................(1)

8%x=4%y+320
multiply by 100
8x=4y+32000

8x-4y=32000
/4
2x-y=8000..................(2)

add (1) & (2)

3x=18000
/3
x=6000 
$6000@8%
$4000@4%