SOLUTION: Carmella Santiago earned 42,000 in book royalties. She invested part at 15% simple interest and the rest at 12%, earning 5,790 per year in interest. How much did she invest at each

Algebra ->  Customizable Word Problem Solvers  -> Finance -> SOLUTION: Carmella Santiago earned 42,000 in book royalties. She invested part at 15% simple interest and the rest at 12%, earning 5,790 per year in interest. How much did she invest at each      Log On

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Question 965166: Carmella Santiago earned 42,000 in book royalties. She invested part at 15% simple interest and the rest at 12%, earning 5,790 per year in interest. How much did she invest at each rate?
I know you have to use I= prt... Right? I just never know how to write it out...

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = amount invested @ 15%
+42000+-+x+ = amount invested @ 12%
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+I+=+P%2Ar%2At+
I think they want +t+=+1+ ( 1 year )
Make this 2 equations:
+I%5B1%5D+=+P%5B1%5D%2Ar%5B1%5D%2A1+
+I%5B2%5D+=+P%5B2%5D%2Ar%5B2%5D%2A1+
+r%5B1%5D+=+15%2F100+
+r%5B2%5D+=+12%2F100+
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Add the equations
+I%5B1%5D+%2B+I%5B2%5D+=+x%2A%28+15%2F100+%29+%2B+%28+42000+-+x+%29%2A%28+12%2F100+%29+
+5790+=+%283%2F20%29%2Ax+%2B+%28+3%2F25+%29%2A%28+42000+-+x+%29+
Now find +x+ and +42000+-+x+