$A$ grouped frequency table with class intervals of equal sizes using $250-270$ ($270$ not included in this interval) as one of the class intervals is constructed for the following data:
$268, 220, 368, 258, 242, 310, 272, 342$
$310, 290, 300, 320, 319, 304, 402, 318$
$406, 292, 354, 278, 210, 240, 330, 316$
$406, 215, 258, 236$
The frequency of the class $310-330$ is:

If the sum of $25$ observations is $900$, find the mean of those observations.

$A$ child says that the median of $3, 14, 18, 20, 5$ is $18$. What does the child not understand about finding the median?

The marks obtained (out of $25$ marks) by $40$ students in an examination are as given below:
$\begin{array}{rrrrrrrrrr} 8, & 12, & 23, & 9, & 5, & 20, & 16, & 3, & 6, & 23 \\ 10, & 6, & 21, & 1, & 18, & 17, & 18, & 16, & 16, & 12, \\ 3, & 15, & 21, & 7, & 12, & 5, & 2, & 7, & 13, & 24, \\ 13, & 18, & 8, & 2, & 20, & 5, & 13, & 7, & 23, & 16 \end{array}$
Represent the data given above by a grouped frequency distribution table,taking the class intervals as $0-5, 5-10, \dots$ etc.

Find the mean of the first seven natural numbers.

For drawing a frequency polygon of a continuous frequency distribution,we plot the points whose ordinates are the frequencies of the respective classes and abscissae are respectively: