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

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Question 977334: melissa invested a sum of money at 3% annual simple interest. she invested three times that sum of 5% annual simple interest. if her total yearly interest from both investments was $3600, how much was invested at 3%?
Answer by richwmiller(17219) About Me  (Show Source):
You can put this solution on YOUR website!
Total yearly interest for the two accounts is: $3600
x=3y+0
0.05*x+0.03*y=3600
Substitute for x
0.05*(3y+0)+0.03*y=3600
Multiply out
0.15y+0+0.03*y=3600
Combine like terms.
0.15y+0+0.03*y=3600
0.15y+0.03*y=3600-0
0.18*y=3600
Isolate y
0.18*y=3600
y=3600/0.18
y=$20000 at 3%
y rounded off
y=$ 20000.00 at 3%
x=3y+0
x=3*20000+0
x=60000+0
x=$60000 at 5%
x rounded off
x=$ 60000.00 at 5%
x=$60000.00 at 5%
y=$20000.00 at 3%
Check
0.05*60000+0.03*20000=3600
3000+600=3600
3600=3600
If this statement is TRUE and neither x nor y is negative then all is well
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