Question

please somebofy answer it

Answer 1

Sn=n/2[2a+ (n-1)d] sum of n terms. [sum of AP formula]

For sum of 25 terms we have:
S(25)=25/2[2a+ (25-1)d] sum of 5 terms.

Sum of 25 terms= 25[a+12d]......................(1)


Now given n th terms =[(n/5)+2]......(2)

a,the first term=(1/5) +2 =11/5 [putting n=1 in.... (2)]
The secound term =12/5 [putting n=2 in..... (2)]

d=2nd term-1st term
=12/5-11/5 =1/5


We got a and d substitute in ....(1)

Sum of 25 terms =25[11/5+12×(1/5)]
=25[23/5] = 5×23=115

Hence option.b is the correct answer.