Math
posted by Joel on .
melissa invested a some of money at 3% annual simple inter she invested 3 times that some at 5 % annual simple interest
if her total yearly interest from both investments was 7200 how much was invested at 3% ?

Invested $X @ 3%.
Invested $3X @ 5%.
0.03X + 0.05*3X = 7200.
0.03X + 0.15X = 7200,
0.18X = 7200.
X = $40,000.