Question

your friend tells you that if you let her keep 20 of your pokemon cards for three months, she will give you 2 cards extra when she returns your cards to you. what is the annual rate of simple interest she is willing to pay for the borrowed cards? note: even though she only keeps your cards for three months, we can still calculate an annual interest rate.

Explanation:

Step1: Define simple interest variables

Let $P=20$ (principal, number of cards borrowed), $I=2$ (interest, extra cards), $t=\frac{3}{12}=0.25$ (time in years). Use simple interest formula $I = P \times r \times t$.

Step2: Rearrange to solve for $r$

$r = \frac{I}{P \times t}$

Step3: Substitute values into formula

$r = \frac{2}{20 \times 0.25}$

Step4: Calculate the rate

$r = \frac{2}{5} = 0.4$, convert to percentage: $0.4 \times 100 = 40$

Answer:

40%