SOLUTION: Use a system of equations in two varibles to solve this problem: A woman invested some money at 8% and some at 9%. The interest on the combined investment of $10,000 was $840.

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Question 328981: Use a system of equations in two varibles to solve this problem:
A woman invested some money at 8% and some at 9%. The interest on the combined investment of $10,000 was $840. How much was invested at 9%
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
A woman invested some money at 8% and some at 9%. The interest on the combined investment of $10,000 was $840. How much was invested at 9%
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let her invest $x at 8%
$y at 9%
..
x+y=10000....................1
0.08x+0.09y=840
multiply by 100
8x+9y=84000..................2
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multiply equation 1 by 8 and subtract equation 2
8x+8y-8x-9y=80000-84000
-y=-4000
y= $4000 the amount investd at 9%
plug the value of y in equation 1
x+4000=10000
x= $6000 amount invested at8%