The median of the data $78, 56, 22, 34, 45, 54, 39, 54, 84$ is

If the marks obtained by the $20$ students are $6, 4, 9, 5, 9, 3, 7, 7, 5, 6, 9, 4, 10, 10, 4, 3, 6, 7, 9, 9$,then the mode of this data is .............

Is it correct to say that in a histogram,the area of each rectangle is proportional to the class size of the corresponding class interval? If not,correct the statement.

The mean of $3, -3, -3, 3, 3, -3$ is ..........

The following are the marks (out of $100$) of $60$ students in mathematics:
$16, 13, 5, 80, 86, 7, 51, 48, 24, 56, 70, 19, 61, 17, 16, 36, 34, 42, 34, 35, 72, 55, 75, 31, 52, 28, 72, 97, 74, 45, 62, 68, 86, 35, 85, 36, 81, 75, 55, 26, 95, 31, 7, 78, 92, 62, 52, 56, 15, 63, 25, 36, 54, 44, 47, 27, 72, 17, 4, 30$
Construct a grouped frequency distribution table with a class width of $10$,such that one of the classes is $10-20$ ($20$ not included).

The facts or figures,which are numerical or otherwise,collected with a definite purpose are called .......