Class 9 · Chapter 12

Statistics

Collection and presentation of data; bar graphs, histograms; measures of central tendency — mean, median, mode.

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Detailed theory

Data is a collection of observations. Raw data (ungrouped) becomes easier to analyse when grouped into a frequency distribution: classes and counts (frequencies). Class mark = midpoint of the class.

Key concepts & formulas

Mean

= (\sum x)/n

Median

=

middle value after sorting.

Mode

=

most frequent value.

Range

=

max

-

min.

Class mark

= (\text{lower} + \text{upper})/2

Frequency: number of times an observation occurs.