If the coefficient of variation and standard deviation of a distribution are $50\%$ and $20$ respectively,what is its mean?

The mean age of $25$ teachers in a school is $40 \text{ years}$. $A$ teacher retires at the age of $60 \text{ years}$ and a new teacher is appointed in his place. If now the mean age of the teachers in this school is $39 \text{ years}$,then the age (in years) of the newly appointed teacher is

The mean and standard deviation of $100$ observations were calculated as $40$ and $5.1$,respectively,by a student who took by mistake $50$ instead of $40$ for one observation. What are the correct mean and standard deviation?

The mean of $100$ items is $49$. It was discovered that three items which should have been $60, 70, 80$ were wrongly read as $40, 20, 50$ respectively. The correct mean is

If both mean and variance of $50$ observations $x_1, x_2, \ldots, x_{50}$ are equal to $16$ and $256$ respectively,then the mean of $(x_1-5)^2, (x_2-5)^2, \ldots, (x_{50}-5)^2$ is

The mean of five observations is $4$ and their variance is $5.2$. If three of these observations are $1, 2$ and $6$,then the other two are