SOLUTION: If you made an extra $9,000. You invested part of the money at 10% and the rest at 8%. You make a total of $840 in interest. How much was invested at 8%?

Question 274183: If you made an extra $9,000. You invested part of the money at 10% and the rest at 8%. You make a total of $840 in interest. How much was invested at 8%?
Answer by fractalier(6550) (Show Source): You can put this solution on YOUR website!
Let x be how much you invest at 8%.
Then 9000 - x is how much you invest at 10%.
Here's the setup...
(.08)x + (.10)(9000 - x) = 840
Multiply by 100 to clear decimals and get
8x + 10(9000 - x) = 84000
8x + 90000 - 10x = 84000
-2x + 90000 = 84000
-2x = -6000
x = 3000
Thus $3000 was invested at 8%.
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