For a given finite $A.P.$,$a=1, l=10$ and $n=10$. Then,$S_{10} = ........$

The sum of the first $20$ terms of the $A.P.$ $1, 21, 41, \ldots$ is:

The sum of the first $n$ terms of an $AP$ whose first term is $8$ and the common difference is $20$ is equal to the sum of first $2n$ terms of another $AP$ whose first term is $-30$ and the common difference is $8$. Find $n$.

The $20^{th}$ term of an $A.P.$ is $40$ and the common difference is $2$. Then,its second term is $\ldots \ldots \ldots \ldots$

Find the $10^{th}$ term of the $A.P.$ $\sqrt{2}, 3 \sqrt{2}, 5 \sqrt{2}, \ldots$ (in $\sqrt{2}$)

The sum of the first $16$ terms of the $AP: 10, 6, 2, \ldots$ is