What is the sum of all natural numbers from $1$ to $100$?

Which term of the A.P. $24, 21, 18,...$ is the first  negative number?

Which term of an A.P. $21, 42, 63,...$ is $210$?

What is the common difference of the A.P. in which $a_{18}-a_{14}=32$?

The sequence of numbers $-10, -6, -2, 2,...$ is

For what value of $p$, $2p+1, 13 \mathrm{and} 5p-3$ are three consecutive terms of an A.P.?

Which term of the A.P. $113, 108, 103,...$ is the first negative number?

${15}^{th}$ term of the A.P. $x-7, x-2, x+3,...$is: