There are 25 people in the calligraphy interest group, and the art group is 20% less than the calligraphy interest group.

25*( 1-20%)=20 people.

There are 25 people in the calligraphy interest group, 25% more than the art interest group. How many students are there in the art interest group?

25 * (1-25%) =18.75 ≈19 people