Which of the following sequences is not an $A.P.$?

The sum of three numbers in $A.P.$ is $48$ and the sum of their squares is $800$. Find those numbers.

The $n^{th}$ term of an $A.P.$ is given by $T_n = 6n - 5$. Then,the $10^{th}$ term of the $A.P.$ is:

For an $A.P.$,the first term is $10$ and the $10^{th}$ term is $100$. Then,the sum of the first $10$ terms is..........

Two $AP$s have the same common difference. The first term of one of these is $-1$ and that of the other is $-8$. Then the difference between their $4^{\text{th}}$ terms is

The students of a school decided to beautify the school on the Annual Day by fixing colourful flags on the straight passage of the school. They have $27$ flags to be fixed at intervals of every $2 \,m$. The flags are stored at the position of the middle-most flag. Ruchi was given the responsibility of placing the flags. Ruchi kept her books where the flags were stored. She could carry only one flag at a time. How much total distance did she cover in completing this job and returning back to collect her books? What is the maximum distance she travelled carrying a flag? (in $m$)