Question

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^Answer the question from the attachment with correct explanation^

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Answer 1

according to the question student plant tree according to their class...
and each class is divided into three sections..

tree planted by class 1

3×1=3
class 2
2*3=6
class 3
3*3=9
class 4
4*3=12
class 5
5*3=15
class 6
6*3=18
class 7
7*3=21
class 8
8*3=24
class 9
9*3=27
class 10
10*3=30
class 11
11*3=33
class 12
12*3=36

total no. of trees are...


3+6+9+12+15+18+21+24+27+30+33+36=
234trees..



sorry for doing so lengthy..


and thank you for the question

Answer 2

Hey friend, Harish here.

Here is your answer:

Trees planted by class 1 = 1 

Trees planted by class 2 = 2
.....

Trees planted by class 12 = 12.

The trees are planted in the series of :

1,2,3,4,5,6,7,8,9,10,11,12 .

Here all have have the same difference that is 1.

Therefore the numbers are in AP.

The first term of AP , a = 1.

Common difference = d = 2 - 1 = 1 . 

Total number of term (n) = 12

We know that,

$S_{n}= \frac{n}{2} \times [2a+(n-1)d]$

→  $S _{12}= \frac{12}{2} \times [ 2(1)+(12-1)(1)]$

→  $S_{12} = 6 \times (2+11)$

→  $S_{12} = 6\times 13$

→  $S_{12} = 78$

So, No of trees planted by 1 section of classes = 78.

      No of trees planted by 3 sections of classes = 78 × 3= 234

Therefore 234 trees are planted by three section of classes .
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Hope my answer is helpful to you.