SOLUTION: A man has three sums of money invested, one at 4 per cent, one at 3 1/2 per cent, and one at 3 per cent.His total annual income from the three investments is $416.The first investm

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Question 495194: A man has three sums of money invested, one at 4 per cent, one at 3 1/2 per cent, and one at 3 per cent.His total annual income from the three investments is $416.The first investment yields $104 more per year than the other two combined.If he could receive 1/2 per cent more on each investment his annual income would be increased by $55.75.How much does he have invested at each rate?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
This looks like simple interest, and not compound interest
Let a = amount invested @ 4%
Let b = amount invested @ 3.5%
Let c = amount invested @ 3%
given:
(1) +.04a+%2B+.035b+%2B+.03c+=+416+
(2) +.04a+=+.035b+%2B+.03c+%2B+104+
(3) +.045a+%2B+.04b+%2B+.035c+=+471.75+
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Multiply both sides of all equations by +1000+
(1) +40a+%2B+35b+%2B+30c+=+416000+
(2) +40a+=+35b+%2B+30c+%2B+104000+
(3) +45a+%2B+40b+%2B+35c+=+471750+
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Divide both sides of all equations by +5+
(1) +8a+%2B+7b+%2B+6c+=+83200+
(2) +8a+=+7b+%2B+6c+%2B+20800+
(3) +9a+%2B+8b+%2B+7c+=+94350+
--------------------------
Rewrite (2) and add it to (1)
(1) +8a+%2B+7b+%2B+6c+=+83200+
(2) +8a+-+7b++-+6c+=+20800+
+16a+=+104000+
+a+=+6500+
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Put this value back into (1)
(1) +8%2A6500+%2B+7b+%2B+6c+=+83200+
(1) +52000+%2B+7b+%2B+6c+=+83200+
(1) +7b+%2B+6c+=+83200+-+52000+
(1) +6c+=+31200+-+7b+
+c+=+5200+-+%287%2F6%29%2Ab+
---------------------
Plug this result into (3)
(3) +9a+%2B+8b+%2B+7c+=+94350+
(3) +9%2A6500+%2B+8b+%2B+7%2A%285200+-+%287%2F6%29%2Ab%29+=+94350+
(3) +58500+%2B+8b+%2B+36400+-+8.1666b+=+94350+
(3) +.1666b+=+58500+-+94350+%2B+36400+
(3) +.1666b+=+550+
+b+=+3300+
-------------
Plug a and b into (1) to find c
(1) +8a+%2B+7b+%2B+6c+=+83200+
(1) +8%2A6500+%2B+7%2A3300+%2B+6c+=+83200+
(1) +52000+%2B+23100+%2B+6c+=+83200+
(1) +6c+=+83200+-+75100+
(1) +6c+=+8100+
+c+=+1350+
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$6,500 = amount invested @ 4%
$3,300 = amount invested @ 3.5%
$1,350 = amount invested @ 3%