Question

Find the value of middle most term(s) of the A.P. -11, -7, -3,.........., 49

Answer 1

$a=-11d=4$

$49=-11+(n-1)4$

$60=4n-4$

$64=4n$

$n=16⟶$ there are 16 terms.

Since the terms are even, there will be $two$ middle most terms.

$\therefore n=8,9$

When $n=8,a_8=17n=9,a_9=21$

$\therefore a_{0,9}=\frac{17+21}{2}=19$