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%. He made a total of $220.00 in interest. How much was invested at 3.25%?
A $4000

B $3000

C $5000

D $3500

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

c. 4 and 1/2 pounds is the answer! : )