The sum of the first $16$ terms of the $A.P.$ $1, 1.5, 2, \ldots$ is:

Write the first three terms of the $APs$ when $a$ and $d$ are as given below:
$a = \sqrt{2}, d = \frac{1}{\sqrt{2}}$

Which term of the $A.P.$ $83, 77, 71, \ldots$ is its first negative term (in $^{th}$)?

Write the first three terms of the $APs$ when $a$ and $d$ are as given below:
$a = -5, d = -3$

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

The ratio of the $11^{\text{th}}$ term to the $18^{\text{th}}$ term of an $AP$ is $2:3$. Find the ratio of the $5^{\text{th}}$ term to the $21^{\text{st}}$ term,and also the ratio of the sum of the first five terms to the sum of the first $21$ terms.