SOLUTION: Roberto invested some money at 7%, and then invested $3000 more than twice this amount at 10%. His total annual income from the two investments was $3810. How much was invested at

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Question 168004: Roberto invested some money at 7%, and then invested $3000 more than twice this amount at 10%. His total annual income from the two investments was $3810. How much was invested at 10%?
P.S. I am assuming that this is to be translated into an actual formula in order to obtain the answer, but I can get really frustrated with almost all word problems. Please help me. Thank you.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Once you call the unknown by a letter, it falls into place, usually
Let x= the amount invested at 7%
Then it gives you
2x+%2B+3000= the amount invested at 10%
Now the problem wants to know how much was made from the 2 investments
Think of this as the profit.
.7x+%2B+.1%2A%282x+%2B+3000%29+=+3810
.7x+%2B+.2x+%2B+300+=+3810
.9x+=+3810+-+300
.9x+=+3510
x+=+3900
This was the amount invested @ 7%
2%2A3900+%2B+3000+=+10800
This was the amount invested @ 10%
check:
.7x+%2B+.1%2A%282x+%2B+3000%29+=+3810
.7%2A3900+%2B+.1%2A10800+=+3810
2730+%2B+1080+=+3810
3810+=+3810
OK
He invested $10,800 @ 10%