Question

Under a project of one child one tree undertaken by the school students to plant the trees in pattern the first two has three plants second row has 7 plant and in the last row has 37 plants to find the number of students

Answer 1

There are three sections of each class and it is given that the number of trees planted by any class is equal to class number.

The number of trees planted by class I = number of sections*1=3*1=3

The number of trees planted by class II = number of sections *2=3*2=6

The number of trees planted by class III = number of sections *3=3*3=9

Therefore, we have sequence of the form 3, 6, 9 … 12 terms

To find total number of trees planted by all the students, we need to find sum of the sequence 3, 6, 9, 12 … 12 terms.

First term = a = 3, Common difference = d= 6 – 3 = 3 and n = 12

Applying formula, Sₙ=n/2[2a+(n-1)d] to find sum of n terms of AP , we get

S₁₂=212/2(6+11*3)

=6(6+33)

=6*39

=234