Question

find the sum of all the 11 terms of an ap whose middle most term is 30​

Answer 1

Given-

*There are 11 terms in an AP

*Middle most term is 30

To find-

sum of all the 11 terms

Solution-

Middle most term of AP of 11 terms = (n+1)/2 = (11+1)/2 = 6th term

a6 = a + 5d

30= a + 5d

a= 30-5d

Now

Sn = n/2{2a+(n-1)d}

S11= 11/2 {2(30- 5d) +(11-1)d}

S11= 11/2 (60-10d+10d)

Therefore, S11= 330

330 is required answer.