If the median and mode of a frequency distribution are $26$ and $29$ respectively, then the mean is

If the mean of $n$ observations $x_1, x_2,......, x_n$ is $\overline{x}$, then the mean of $x_{1-a}, x_{2-a},......, x_{n-a}$ is

Note: This question given in the book seems to have errors and the modified question should be as given below:

If the mean of $n$ observations $x_1, x_2,......, x_n$ is $\overline{x}$, then the mean of $x_1-a, x_2-a,......, x_n-a$ is

If the mean of first $n$ odd natural numbers is $\frac{n^2}{81}$, then $n$ is equal to

The mean of first $n$ odd natural numbers is

Consider the following frequency distribution:

The modal class is