When simplifying a fraction, why is it mathematically correct to cancel a common factor like $5$ from both the numerator and the denominator?

Because subtracting $5$ from the top and bottom is a valid step.

Because the operation is equivalent to dividing by $ \frac{5}{5} $, which equals 1.

Because it is the smallest common factor.

Using Prime Factorization to Reduce Fractions Practice — Grade 6 math