Final answer:
To calculate the amount Madeline will have in 3 years with a 20% interest rate, we use the simple interest formula A = P(1 + rt). Plugging in the values, Madeline will have $20.8 in her savings account.
Step-by-step explanation:
To calculate the amount Madeline will have in 3 years, we need to use the simple interest formula which is: A = P(1 + rt), where A is the final amount, P is the principal amount, r is the interest rate, and t is the time in years. In this case, Madeline's principal amount is $13, the interest rate is 20% per year (0.2), and the time is 3 years.
A = 13(1 + 0.2 * 3) = 13(1 + 0.6) = 13(1.6) = $20.8
Therefore, Madeline will have $20.8 in her savings account in 3 years.