Question

In a school, it was decided that the no. of trees that each section of each class will plant, will be double of the class in which they r studying. If there are 1 to 12 classes in the school and each class has 2 sections, find how many trees were planted by the students.

please friends solve it n tell me the answer..!.....my answer is 312 but i'm not sure about it..!!
HELP ME OUT..!!

Answer 1

Each section of each class will plant double the number of the class in which they are studying.

That means
each section of class 1 will plant= 1*2 = 2 trees, 
each section of class 2 will plant = 2*2 = 4 trees,
each section of class 3 will plant = 3*2 = 6 trees and so on.

Each class has 2 sections. 
So class 1 will plant 2*2 = 4 trees
class 2 will plant = 4*2 = 8 trees
class 3 will plant  = 6*2 = 12  trees and so on...

It is an AP with first term a=4, common difference, d = 8-4 = 4 and total 12 terms.

So total number of plants is

$S_n = \frac{n}{2}[2a+(n-1)d]\\ \\S_n=\frac{12}{2}[2 \times 4+(12-1) \times 4]\\ \\S_n=6[8+44]=6 \times52\\ \\S_n=312$

Thus 312 trees were planted by students.