SOLUTION: Rhianna invests $1200 in stock and bonds. The stock pays 9% interest and the bonds pay 6% interest. If the total ANNUAL interest is $96, how much is invested in the stock alone?

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Question 970699: Rhianna invests $1200 in stock and bonds. The stock pays 9% interest and the bonds pay 6% interest. If the total ANNUAL interest is $96, how much is invested in the stock alone?

A)
$400

B)
$500

C)
$700

D)
$800
Answer by MathLover1(20850) About Me  (Show Source):
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Rhianna invests $1200 in stock s and bonds b.
The stock pays 9%25+ =0.09 interest and the bonds pay 6%25=0.06 interest.

.09s+%2B+.06b+=+96.........eq.1
s+%2B+b+=+1200.........eq.2
----------------------------------------------------
from eq.2
b+=+1200-s.......substitute in eq.1
.09s%2B+.06%281200-s%29++=+96.............solve for s
.09s%2B+72-0.06s++=+96
.09s-0.06s++=+96-72
.03s++=+24
s++=+24%2F0.03
s++=+2400%2F3
s++=+800
If the total ANNUAL interest is $I=96, in the stock alone is invested $+highlight%28800%29.
then, in the bond is invested $+1200-800=400
check:
The stock pays 9%25+ of $+800:
$+800%2A0.09=72

The bond pays 6%25+ of $+400:
$+400%2A0.06=24
then, 72%2B24=96 which confirms our solution

so, answer is
D)
$800