SOLUTION: Equal amounts are invested at 5%,7%, and 9% annual interest. If the three investments yield a total of $840 annual interest , find the total investment.

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Question 1163730: Equal amounts are invested at 5%,7%, and 9% annual interest. If the three investments yield a total of $840 annual interest , find the total investment.
Found 2 solutions by ikleyn, greenestamps:
Answer by ikleyn(52786) About Me  (Show Source):
You can put this solution on YOUR website!
.

0.05x + 0.07x + 0.09x = 840   dollars  (total interest equation).


0.21x = 840


x = 840%2F0.21 = 4000 dollars invested to each account, in all  12000 dollars.    ANSWER



Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


Equal amounts invested at 5%, 7%, and 9% means the average rate is 7%, because 7% is halfway between 5% and 9%.

.07%28x%29+=+840
x+=+840%2F.07+=+12000

ANSWER: The amount invested was $12,000.

CHECK: .05(4000)+.07(4000)+.09(4000) = 200+280+360 = 840