The mean of the data $\frac{4}{7}, \frac{4}{9}, \frac{3}{7}, \frac{5}{9}$ is ........

The following observations are arranged in ascending order:
$26, 29, 42, 53, x, x+2, 70, 75, 82, 93$
If the median is $65,$ find the value of $x$.

The mean marks (out of $100$) of boys and girls in an examination are $70$ and $73$,respectively. If the mean marks of all the students in that examination is $71$,find the ratio of the number of boys to the number of girls.

The mean of $35$ observations is $42$. Find the sum of those observations $\left(\Sigma f_{i} x_{i}\right)$.

If $\bar{x}$ is the mean of $x_{1}, x_{2}, \ldots, x_{n},$ then for $a \neq 0,$ the mean of $a x_{1}, a x_{2}, \ldots, a x_{n}, \frac{x_{1}}{a}, \frac{x_{2}}{a}, \ldots, \frac{x_{n}}{a}$ is

Find the mean of the observations $15, 22, 18, 27, 31, 21, 14, 36, 25$ and $34$.