Grasping the invariants, the boys here have not changed, and the boys are also considered as unit one.

The number of girls in the art group is 3/ 10, and there are 7 boys, of whom 3/7 are girls.

Later, five girls took part. At this time, girls in the art group accounted for two-fifths of the number of people in the art group. At this time, there are three boys, and the girls are two-thirds of the boys, with a difference of 2/3-3/7 = 5/2 1, corresponding to five people, and the boys are 5/5/2 1 = 265438+.

Now the number of people is 21× 2/3 =14+21= 35.