If $2, x, 20$ are three consecutive terms of an $A.P.$,then $x = ..........$

Which term of the $A.P.$ $20, 19 \frac{1}{4}, 18 \frac{1}{2}, 17 \frac{3}{4}, \ldots$ is its first negative term (in $^{th}$)?

The $n^{th}$ term of an $A.P.$ is given by $T_n = 5n - 2$. Then,the $12^{th}$ term of the $A.P.$ is:

Which term of the $A.P.$ $112, 107, 102, \ldots$ is its first negative term?

Determine whether the following sequence is an $A.P.$ or not. (Assume that the pattern continues.) If it is an $A.P.$,find its $n^{th}$ term: $1, 4, 9, 16, \ldots $

$3+6+9+12+\ldots+300 = \ldots$