SOLUTION: Paul and Donna Petrie invested $12,000 part at 5% simple interest and the rest a 7% simple interest for a period of 1 year. How much did they invest at each rate if their total an

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Question 659057: Paul and Donna Petrie invested $12,000 part at 5% simple interest and the rest a 7% simple interest for a period of 1 year. How much did they invest at each rate if their total annual interest from both investments was $800? (Use interest= principal x rate x time.)
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
interest= principal x rate x time
Let +x+ = amount invested at 5%
+12000+-+x+ = amount invested at 7%
+I%5B1%5D+=+x%2A.05%2A1+
+I%5B1%5D+=+.05x+
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+I%5B2%5D+=+%28+12000+-+x+%29%2A.07%2A1+
+I%5B2%5D+=+840+-+.07x+
-------------------
+I%5B1%5D+%2B+I%5B2%5D+=+800+
+.05x+%2B+840+-+.07x+=+800+
+-.02x+=+-40+
+x+=+2000+
+12000+-+x+=+12000+-+2000+
+12000+-+x+=+10000+
$2,000 = amount invested at 5%
$10,000 = amount invested at 7%