The width of the class $50.5-55.5$ is .............

Find the median of the observation: $62, 67, 82, 71, 75, 77, 63, 91$.

The mean of the observations $x+5$,$x+3$,$x+11$,and $x+1$ is ..........

The mean of $10$ observations is $16.5$. It was later noticed that one observation was taken as $57$ instead of $75$ by mistake. Find the correct mean of the data.

Find the mode of the following observations: $14, 25, 28, 29, 17, 14, 19, 22, 14, 30, 16, 28, 14, 25$.

The mean of $25$ observations is $36$. If the mean of the first $13$ observations is $32$ and the mean of the last $13$ observations is $40$,find the $13^{\text{th}}$ observation.