Question

In a school, students thought of planting trees in and around the school to reduce air
pollution. It was decided that the number of trees, that each section of each class will
plant will be the same as the class, in which they are studying, e.g., a section of Class 1 a section of class 2 will plant 2 trees and so on till Class XII. There are
three sections of each class. How many trees will be planted by the students?​

Answer 1

Hey here us your answer hope it helps........

Answer 2

Given

there are three sections in each class.

there are 12 classes

if you are in class 1 you will plant 1 tree.

and so on.........

so number of trees planted by class 1 will be 1 x number of sections

that is 1 x 3 = 3

Similarly  

number of trees planted by class 2 = 2 x 3 = 6

number of trees planted by class 3 = 3 x 3 = 9

............

number of trees planted by class 12 = 12 x 3 = 36

The sequence will be 3,6,9,........,36.

This in an AP cause the difference between all the terms remains the same.

d = 3

So the total number of trees planted will be as follows..........

Sn= n/2 [2a+(n-1)d]

S12 = 12/2 [6+(12 - 1)(3)]

S12 = 6(6+33) = 6 39 = 234

234 is the total number if trees planted.