- The information collected in term of numbers is called data.
- Data are represented graphically to have a quick glance on them.
- Data available in an unorganised form are called raw data.
- The number of times a particular observation occurs in a given data is called its frequency.
- When the data are large, they can be arranged in groups and each group is known as Class Interval or Class.
- A table showing the frequencies of various observations or class intervals of a given data is called a Frequency Distribution table.
- The upper value of a class interval is called its Upper Class Limit and the lower value of the class interval is called its Lower Class Limit.
- The difference between the upper class limit and lower class limit of a class is called the Width or Size of the class.
- The difference between the lowest and the highest observation in a given data is called its Range.
- Grouped data can be represented by a histogram.
- Histogram is a type of bar diagram, where the class intervals are shown on the horizontal axis and the heights of the bars (rectangles) show the frequency of the class interval, but there is no gap between the bars as there is no gap between the class intervals.
- Data can also be represented using a pie chart (circle graph).
- It shows the relationship between a whole and its parts.
- There are certain experiments whose outcomes have an equal chance of occurring. Such outcomes are said to be equally likely.
- Probability of an event = Number of outcomes that make an event , Total number of outcomes of the experiment when the outcomes are equally likely.

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