**Important Concepts and Formulas**

1. Data is a collection of numbers,
figures, names or any items collected to give some information.

3. Data can be collected by the
following methods: Taking measurements in experiments, Observing outcomes of
events, conducting surveys, reading statistical publications.

4. The difference between the highest
and the lowest observations is called the range of the data. Range = Value of
the highest observation – Value of the lowest observation.

5. Arithmetic mean is obtained by
dividing the sum of all observations by the number of observations. For a data
set of n items, x

_{1}, x_{2}, ... , x_{n}, mean = (x_{1}+ x_{2}+ … x_{n})/n.
7. If N is odd, the median = the middle
term. For example, for {1, 3, 6, 8, 9, 10, 17}, the median = 8.

8. If N is even, the median = the mean
of the two middle terms. For example, for {4, 7, 10, 13, 15, 20}, the median =
½ (10 + 13) = 11.5.

10. To represent data using a bar graph,
we have to draw bars or rectangles of uniform width leaving equal space
in-between the rectangles. The length of the bars represents the required
information about the quantity.

11. Bar graphs can be easily drawn and
drawing them is less time consuming.