SOLUTION: You have already invested $350 in a stock with an annual return of 11%. How much of an additional $800 should be invested at 12% and how much at 6% so that the total return on the

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Question 511299: You have already invested $350 in a stock with an annual return of 11%. How much of an additional $800 should be invested at 12% and how much at 6% so that the total return on the entire $1,150 is 9%? (Round each answer to the nearest cent.)

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let a = amount invested @ 12%
Let b = amount invested @ 6%
given:
++.11%2A350+=+38.5 is Return on $350 @ 11%
+.09%2A1150+=103.5+ is return on $1150 @ 9%
--------------
(1) +a+%2B+b+=+800+
(2) +38.5+%2B+.12a+%2B+.06b+=+103.5+
------------------------
Multiply both sides of (2) by 100
(2) +3850+%2B+12a+%2B+6b+=+10350+
(2) +12a+%2B+6b+=+6500+
(2) +6a+%2B+3b+=+3250+
Multiply both sides of (1) by +3+ and
subtract (1) from (2)
(2) +6a+%2B+3b+=+3250+
(1) +-3a+-+3b+=+-2400+
+3a+=+850+
+a+=+283.33+
and, since
+a+%2B+b+=+800+
+b+=+800+-+283.33+
+b+=+516.67+
$283.33 should be invested @ 12% and
$516.67 should be invested @ 6%
check:
(2) +38.5+%2B+.12%2A283.33+%2B+.06%2A516.67+=+103.5+
(2) +38.5+%2B+34+%2B+31+=+103.5+
(2) +103.5+=+103.5+
OK