Answer: A $4000
Step-by-step explanation:
Let x represent the amount which he invested at 3% interest.
Let y represent the amount which he invested at 3.25% interest.
Walt made an extra $7000 last year from a part-time job. He invested part of the money at 3% and the rest at 3.25%. This means that
x + y = 7000
The formula for determining simple interest is expressed as
I = PRT/100
Considering the account paying 3% interest,
P = $x
T = 1 year
R = 3℅
I = (x × 3 × 1)/100 = 0.03x
Considering the account paying 3.25% interest,
P = $y
T = 1 year
R = 3.25℅
I = (y × 3.25 × 1)/100 = 0.0325y
He made a total of $220.00 in interest., it means that
0.03x + 0.0325y = 220 - - - - - - - -- -1
Substituting x = 7000 - y into equation 1, it becomes
0.03(7000- y) + 0.0325y = 220
210 - 0.03y + 0.0325y = 220
- 0.03y + 0.0325y = 220 - 210
0.0025y = 10
y = 10/0.0025
y = 4000
