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.
To find out how much Melissa invested at 3%, we can use the concept of simple interest.
Let's denote the amount she invested at 3% as 'x'. According to the problem, she invested 3 times that amount (3x) at 5%.
To calculate the interest earned from each investment, we can use the formula: Interest = Principal × Rate × Time.
For the investment at 3%:
Interest1 = x × 0.03 × 1 (Considering 1 year as the time)
For the investment at 5%:
Interest2 = 3x × 0.05 × 1 (Again, 1 year as the time)
Given that the total yearly interest from both investments was $7200, we can form the equation:
Interest1 + Interest2 = 7200
Substituting the values, we get:
x × 0.03 × 1 + (3x) × 0.05 × 1 = 7200
Simplifying this equation:
0.03x + 0.15x = 7200
0.18x = 7200
x = 7200 / 0.18
x = 40000
Therefore, Melissa invested $40,000 at 3%.