SOLUTION: Melissa invested a sum of money at 3% annual simple interest. She invested three times that sum at 5% annual simple interest. If her total yearly interest from both investments was

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Question 105817: Melissa invested a sum of money at 3% annual simple interest. She invested three times that sum at 5% annual simple interest. If her total yearly interest from both investments was $7200, how much was invested at 3%?
Answer by checkley75(3666) About Me  (Show Source):
You can put this solution on YOUR website!
.03X+.05(3X)=7200
.03X+.15X=7,200
.18X=7,200
X=7,200/.18
X=40,000 IS THE AMOUNT INVESTED @ 3%
3*40,000=120,000 INVESTED @ 5%
PROOF
.03*40,000+.05*120,000=7200
1,200+6,000=7,200
7,200=7,200