Find the sum of all the 11 terms of an AP whose middle most term is 30.
No of terms = 11 as it is even
Middle term will be 
i.e. 6th term
Let the first term be a and common difference be d of an AP
As
an = a + (n - 1)d
a6 = a + (6 - 1)d
30 = a + 5d [ eqn 1]
Now as we know,
[ using eqn 1]
30