A school organizes extracurricular activity groups. The personnel of the three groups are distributed as follows (each student only participates in one group): Chess group.

(1) According to the meaning of the question, the total number of the three groups is X,

The photography team * * * has 18+ 12=30 people, and 3 people are selected.

Then 330 = 6x,

The solution is available, x=60,

Then a = 60-30-6-4-7 =13;

So a = 13.

(2) Calligraphy group ***6+4= 10,

Three people were randomly selected from the calligraphy group 10, and * * there were C3 10 = 120 methods.

All three students are junior high school students and senior high school students, including two junior high school students 1 and two junior high school students 1.

* * * There are c16c24+c16c14 = 96 methods;

We take "the calligraphy group randomly selects three people to participate in the calligraphy competition, among whom three are junior and senior high school students" as event A,

Then p (a) = 96 120 = 45.