Total probability

Question

There are three groups in the class. Each group contains a different number of students. The first group has 15 students, out of which 8 are girls. The second group has 9 students, out of which the girls are 4. The third group has 12 students, out of which 7 are girls. Find the probability of selecting a girl randomly from one of the three groups

Answer 1

Banu Annan ponnu, hello

What you did not tell us is what is the probability of selecting one of the groups?  Is it just as probable so select from any of the three groups?  If it is, then you are really just asking what is the probability of selecting one of 19 girls from a group of 36 students; probability is approximately 0.528 in that case.

Otherwise you have to give us the probability of selecting each of the three groups.