SOLUTION: Lillian is about to invest $20,000, part at 3% and the rest at 4%. What is the most that she can invest at 3% and still be guaranteed atleast $650 in interest per year? Thank you!

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Question 558774: Lillian is about to invest $20,000, part at 3% and the rest at 4%. What is the most that she can invest at 3% and still be guaranteed atleast $650 in interest per year? Thank you!
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
x + y 20000 ------------------------1
3.00% x + 4.00% y = $650.00
Multiply by 100
3 x + 4 y = $65,000.00 --------2

Multiply (1) by -3
we get

-3 x -3 y = -60000.00

Add this to (2)

y = $5,000.00

investment at 4.00%
Balance $15,000.00 investment at 3.00%
CHECK
$15,000.00 $450.00
$5,000.00 $200.00
Total $650.00