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Question:

In a school, students decided to plant 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 double the class in which they are studying. If there are 1 to 12 classes in the school and each class has two sections, find how many trees were planted by the students. Which value is shown in this question?

Solution:

Class 1 will plant=2×1×2=4treesClass 2 will plant=2×2×2=8treesClass 3 will plant=2×3×2=12treesClass 4 will plant=2×4×2=16treesClass 5 will plant=2×5×2=20treesSimilarly for 12 will plant=2×12×2=48treesSo,4,8,12,16,2048are in A.P.Herea=4,n=12,l=48We know thatSn=n2[a+l]Sn=122[4+48]Sn=6×52Sn=312Hence,312trees planted by the students.