Answer: she invested $17000 in the account earning 6% annual interest.
she invested $13000 in the account earning 7.5% annual interest.
Explanation:
Let x represent the amount that she invested in the account earning 6% annual interest.
Let y represent the amount that she invested in the account earning 7.5% annual interest.
Marilyn Mallinson invested $30000, part at 6% annual interest and the rest at 7.5% annual interest. This means that
x + y = 30000
The formula for determining simple interest is expressed as
I = PRT/100
Where
I represents interest paid on the loan.
P represents the principal or amount taken as loan
R represents interest rate
T represents the duration of the loan in years.
Considering the account earning 6% annual interest.
P = x
R = 6%
T = 1 year
I = (x × 6 × 1)/100 = 0.06x
Considering the account earning 7.5% annual interest,
P = y
R = 7.5
T = 1
I = (y × 7.5 × 1)/100 = 0.075y
Last year she earned $1995 in interest. This means that
0.06x + 0.075y = 1995 - - - - - - - -
Substituting x = 30000 - y into equation 1, it becomes
0.06(30000 - y) + 0.075y = 1995
1800 - 0.06y + 0.075y = 1995
- 0.06y + 0.075y = 1995 - 1800
0.015y = 195
y = 195/0.015 = 13000
x = 30000 - y = 30000 - 13000
x = 17000