SOLUTION: Question: Suppose you invested $10,000, part at 6% annual intrest and the rest at 9% annual intrest. If you received $684 in intrest after on year, how much did you invest at e

Question 2371: Question: Suppose you invested $10,000, part at 6% annual intrest and the rest at 9% annual intrest. If you received $684 in intrest after on year, how much did you invest at each rate?
Answer by longjonsilver(2297) (Show Source): You can put this solution on YOUR website!
First define...
Let x = amount invested at 6% rate
Let y = amount invested at 9% rate
so, after 1 year, 0.06x + 0.09y = 684 --eqn1
Also, we know that x+y=10000 --eqn2
Eqn2 is re-written as x=10000-y, and then sub this into eqn1, to give
0.06(10000-y) + 0.09y = 684
600 - 0.06y + 0.09y = 684
0.03y = 84
y = 2,800
so, x= 7200
jon.

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