First term a = 1
Second term t1 = 2
Third term t3 = 3
Common difference d = t3 – t2 = 3 – 2 = 1
We need to find total number of trees when n = 25
Thus, by using sum of nth term of an A.P. we will find its sum
Where, n = no. of terms
a = first term
d = common difference
Sn = sum of n terms
We need to find S25
Thus, on substituting the given value in formula we get,