For a given finite $A.P.$,$a=2, n=8$ and $S_{8}=72$. Then,$l=........$

The measures of all the four angles of a quadrilateral form an $A.P.$. If the common difference is $10^{\circ}$,find the measures of all the angles.

$A$ plastic toy consists of $14$ circular discs of different radii. The radius of the smallest disc is $1\, cm$, the radius of the next bigger disc is $2\, cm$, and so on, such that the radius of the biggest disc is $14\, cm$. Find the sum of the circumferences of all the discs in $cm$.

The $n^{th}$ term of an $A.P.$ is given by $T_{n} = 4n + 7$. Find the sum of $n$ terms of this $A.P.$

Find the sum of those integers from $1$ to $500$ which are multiples of $2$ or $5$.

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