In a group photograph, 6 teachers and principal are in the first row and 18 students are in the second row. There are 12 boys and 6 girls among the students. If the middle position is reserved for the principal and if no two girls are together, find the number of arrangements.

On the World Environment Day tree plantation programme was arranged on a land which is triangular in shape. Trees are planted such that in the first row there is one tree, in the second row there are two trees, in the third row there are three trees and so on. Then find the total number of trees in 25 rows.

Suppose there is a co-education school having 60% boys and 40% girls as students. The girl students have secured first class and second class in equal numbers and all boys secrured first class. A teacher selects a student at random and verifies the result. teacher observes thata student has secured first class in the examination. What is the probability that the student is a girl?

A teacher wanted to reward a student by giving some chocolates. He gave the students two choices. He could either have 60 chocolates at once or he could get 1 chocolate on the first day, 2 on the second day, 4 on the third day and so on for 6 days, which option should the student chose to get more chocolates.