You lend your friend $240. He gives you back $270. What interest rate did you charge your friend?
To determine the interest rate charged, we need to find the difference between the amount repaid and the amount lent.
$270 - $240 = $30
The interest charged is $30.
Next, we need to find the percentage of the interest charged out of the original amount lent:
($30 / $240) x 100 = 12.5%
Therefore, the interest rate charged to the friend is 12.5%.