Libby is incorrect. To simplify a fraction, we need to find the greatest common divisor (GCD) of the numerator and the denominator and then divide both the numerator and the denominator by the GCD. In this case, the GCD of 12 and 15 is 3. If we divide both 12 and 15 by 3, we get 4/5. Therefore, 12/15 can be simplified to 4/5.
