Six numbers are in an $AP$ such that their sum is $3$. The first term is $4$ times the third term. Then, the fifth term is:

If the $7^{th}$ term of an $A.P.$ is $40$,then the sum of the first $13$ terms is:

Find the sum of all natural numbers lying between $100$ and $1000$ which are multiples of $5.$

If $3^{2 \sin 2 \alpha - 1}$,$14$,and $3^{4 - 2 \sin 2 \alpha}$ are the first three terms of an $A.P.$ for some $\alpha$,then the sixth term of this $A.P.$ is

For $p, q \in R$,consider the real-valued function $f(x) = (x - p)^2 - q$,where $x \in R$ and $q > 0$. Let $a_1, a_2, a_3, a_4$ be in an arithmetic progression with mean $p$ and a positive common difference $d$. If $|f(a_i)| = 500$ for all $i = 1, 2, 3, 4$,then the absolute difference between the roots of $f(x) = 0$ is:

Let $a_{1}, a_{2}, \ldots, a_{21}$ be an $A.P.$ such that $\sum_{n=1}^{20} \frac{1}{a_{n} a_{n+1}} = \frac{4}{9}$. If the sum of this $A.P.$ is $189$,then $a_{6} a_{16}$ is equal to: