Final answer:
To calculate the interest rate for Marie's account, we use the formula I = P × r × t. With $8 interest over 2 years from a $200 initial deposit, we find that the rate is 2% per annum.
Step-by-step explanation:
To determine the interest rate for Marie's savings account, we use the simple interest formula, which is given by I = P × r × t, where I is the interest earned, P is the principal amount (initial amount of money), r is the annual interest rate, and t is the time in years the money is invested or borrowed for.
In Marie's case, she has earned $8 in interest over 2 years from an initial deposit of $200. Substituting the known values into the formula:
I = P × r × t
$8 = $200 × r × 2
We can solve for r by dividing both sides of the equation by $200 × 2.
r = $8 / ($200 × 2)
r = $8 / $400
r = 0.02
So, the annual interest rate is 0.02, or when expressed as a percentage, 2%.