SOLUTION: John had $30,000 to invest. He invested part of this money in bonds paying 12% annual simple interest and the rest of the money in a savings account giving 4% annual interest. At t

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Question 959253: John had $30,000 to invest. He invested part of this money in bonds paying 12% annual simple interest and the rest of the money in a savings account giving 4% annual interest. At the end of the year, he received
$2,400 as extra income. How much money did John place in each investment?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +x+ = amount invested @ 12%
+30000+-+x+ = amount invested @ 4%
+I%5B1%5D+=+P%2Ar%2At+
+I%5B1%5D+=+x%2A.12%2A1+
+I%5B1%5D+=+.12x+
and
+I%5B2%5D+=+P%2Ar%2At+
+I%5B2%5D+=+%28+30000+-+x+%29%2A.04%2A1+
+I%5B2%5D+=+1200+-+.04x+
and
+I%5B1%5D+%2B+I%5B2%5D+=+2400+
by substitution:
+.12x+%2B+1200+-+.04x+=+2400+
+.08x+=+1200+
+x+=+15000+
+30000+-+x+=+15000+
-----------------------
He invested $15,000 in both
check:
+I%5B2%5D+=+1200+-+.04x+
+I%5B2%5D+=+1200+-+.04%2A15000+
+I%5B2%5D+=+1200+-+600+
+I%5B2%5D+=+600+
and
+I%5B1%5D+=+.12x+
+I%5B1%5D+=+.12%2A15000+
+I%5B1%5D+=+1800+
----------------
+I%5B1%5D+%2B+I%5B2%5D+=+2400+
+600+%2B+1800+=+2400+
+2400+=+2400+
OK