The mean of the numbers $a, b, 8, 5, 10$ is $6$ and the variance is $6.80$. Then which one of the following gives possible values of $a$ and $b$?

If the standard deviation of $0, 1, 2, 3, \dots, 9$ is $K$,then the standard deviation of $10, 11, 12, 13, \dots, 19$ is

The standard deviation and mean of five observations are $0$ and $9$ respectively. If one of the observations is changed such that the mean of the new set of five observations becomes $10$,then their standard deviation is

The variance of the data $2, 4, 6, 8, 10$ is

The following is the record of goals scored by team $A$ in a football session:

No. of goals scored	$0, 1, 2, 3, 4$
No. of matches	$1, 9, 7, 5, 3$

For team $B$,the mean number of goals scored per match was $2$ with a standard deviation of $1.25$ goals. Find which team may be considered more consistent?

If each of the observations $x_{1}, x_{2}, \ldots, x_{n}$ is increased by $a$,where $a$ is a positive or negative number,show that the variance remains unchanged.