Forty-six students in a class signed up for four extracurricular activity groups: mathematics, art, calligraphy and composition.

A stands for mathematics, B stands for art, C stands for calligraphy, and D stands for composition, so 1 All the situations that students take part in are A, B, C, D, AB, AC, AD, BC, BD, ABC, Abd, ACD, and they are all equally possible, so 46/ 12.