SOLUTION: Alberto invested $15000, part at 6.5% annual interest and rest at 9%. If his annual income from both investments was $1200, how much was invested at each rate?

Question 775269: Alberto invested $15000, part at 6.5% annual interest and rest at 9%. If his annual income from both investments was $1200, how much was invested at each rate?
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
Part I 6.50% per annum ------------- Amount invested =x
Part II 9.00% per annum ------------ Amount invested = y
15000
Interest----- 1200.00

Part I 6.50% per annum ---x
Part II 9.00% per annum ---y
Total investment
x + 1 y= 15000 -------------1
Interest on both investments
6.50% x + 9.00% y= 1200
Multiply by 100
6.5 x + 9 y= 120000.00 --------2
Multiply (1) by -6.5
we get
-6.5 x -6.5 y= -97500.00
Add this to (2)
0 x 2.5 y= 22500
divide by 2.5
y = 9000
Part I 6.50% $ 6000
Part II 9.00% $ 9000

CHECK
6000 --------- 6.50% ------- 390.00
9000 ------------- 9.00% ------- 810.00
Total -------------------- 1200.00

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