Question 442265: How do I solve this problem?
A $132,000 trust is to be invested in bonds paying 6%, CDs paying 5%, and mortgages paying 7%. The bond and CD investment together must equal the mortgage investment. To earn a $8420 annual income from the investments, how much should the bank invest in bonds?
Answer by mananth(16946)   (Show Source):
You can put this solution on YOUR website! Bonds --- 6% ----- x
CD's -----5%-------y
Mortages--7%------x+y
...
Interest to be earned = $8420
Investment = 132,000
x+y+x+y = 132,000
2x+2y=132000
x+y = 66,000.........1
6x+5y+7(x+y) = 8420*100
6x+5y+7x+7y=8420*100
13x+12y=8420*100......2
.........
x+y=66000 .............1
13x+12y=842000 .............2
Eliminate y
multiply (1)by -12
Multiply (2) by 1
-12x-12y =-792000
13x+12y= 842000
Add the two equations
x=50000 investment in Bonds
plug value of x in (1)
x +y = 66000
50000 +y = 66000
y = 66000 -50000
y = 16000
y = 16000 Investment in CD's
Mortage = 66,000
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