Question

What is the sum of 11 terms of A.P. whose middle term is 30?

Answer 1

Note:
1)middle term of AP=(fist term + lat term)/2
2)Sum of n terms of an ap=n(1st term+n th term)/2

Solution:
n = 11
Equation to find the middle term=(a1+a11)/2
Also, given that middle term=30
Therefore,
(a1+a11)/2 = 30
(a1+a11)= 60---(1)

Sum of 11 terms of AP = 11(a1+a11)/2
From (1) we get a1+a11=60

Sum = 11×60/2
= 11×30
= 330

Answer)330