A box contains 60 apples. If one-fifth of the apples are rotten, what percent of the apples are rotten?

One-fifth of 60 apples is (1/5) * 60 = <<(1/5)*60=12>>12 apples.

To find the percentage, we divide the number of rotten apples by the total number of apples and multiply by 100: (12/60)*100 = 20%.
Therefore, 20% of the apples are rotten. Answer: \boxed{20}.