If the sum of the first $n$ terms of a series is $5n^2 + 2n$,then its second term is

Let $a_{1}, a_{2}, a_{3}, \ldots$ be a $G$.$P$. such that $a_{1} < 0$; $a_{1} + a_{2} = 4$ and $a_{3} + a_{4} = 16$. If $\sum_{i=1}^{9} a_{i} = 4 \lambda$,then $\lambda$ is equal to:

Three numbers are in $G.P.$ such that their sum is $38$ and their product is $1728$. The greatest number among them is

The sixth $H.M.$ between $3$ and $\frac{6}{13}$ is

If $a_1 = a_2 = 2$ and $a_n = a_{n-1} - 1$ for $n > 2$,then $a_5$ is:

The $n^{th}$ term of the series $\frac{1}{1} + \frac{1 + 2}{2} + \frac{1 + 2 + 3}{3} + \dots$ will be