(2) Number of first-year students: 90+ 100= 190 (person), number of second-year students:110+120 = 230 (person), number of third-year students:/kloc.

A: The number of first-year students is the least;

(3)( 190+230+2 10)÷3

=630÷3,

=2 10 (person),

A: On average, there are 265,438+00 students in each grade.

(4)( 120-90)÷ 120

=30÷ 120,

=0.25,

=25%,

A: Girls in Grade Three are 25% less than boys.

So the answers are: (2) senior one, (2)2 10, (3) 25.