The class mark of the class $70-90$ is ...........

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:

The mean of the $10$ observations is $68$. If each observation is divided by $2$ and then $6$ is added to each result, find the mean of the new observations so obtained.

Classifying the observations $0, 3, 2, 5, 7, 8, 10, 12, 5, 6, 6, 4, 14, 18, 20$ of a data,the frequency of class $0-5$ is ........

To present a large amount of data so that a reader can make sense of it easily,the variable values are condensed into groups called ..........

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