### CHAPTER AT A GLANCE

**1. Basic Term**

**(I) Class limits: **Suppose marks obtained by all of the students are divided into class intervals 25 – 35, 35 – 45 and so interval on.

In class 25-35,25 is called lower class limit and 35 is called upper class limit.

**(ii)Class size :** The difference between upper and lower class limit.

**(iii) Class mark: **It is given by

**2. Ungrouped and Grouped Data**

The data obtained in original form are called raw data or ungrouped data.

To put the data in a more condensed form, we make groups of suitable size and mention the frequency of each group. Such a table is called a grouped frequency distribution table, and the data so obtained is called grouped data.

**3. Mean**

**4. Mode**

**5. Median**The median

**is a measure of central tendency which gives the value of the middle most observation in the data.**

**6. Relationship Between Mean, Mode and Median**

3 Median = Mode + 2 Mean

**7. Cumulative Frequency Curve (Ogive)**

**(i)** The smooth free hand curve is formed by joining the points (xi, fi;) where xi is the upper limit of a class and t;, is the corresponding c.f. The curve so obtained is called a cumulative frequency curve, or an ogive of the less than type.

**(ii)** The smooth free hand curve is formed by joining the points (xi, t;;) where xi is the lower limit of a class and t;, is the corresponding c.f. The curve so obtained is called a cumulative frequency curve, or an ogive of the more than type.

**8. Median by Graph**

**(I)** Draw the ogive of the less than type and ogive of the more than type on the same axis. The two ogives will intersect each other at a point. From this point, if we draw a perpendicular on the x-axis, the point at which it cuts the x-axis gives us the median.

**(ii)** Draw the ogive of the less than type, then locate n/2 on the y-axis

(n = number of observations). From this point on y-axis, draw a line parallel to x-axis cutting the less than ogive at a point. From this point draw a perpendicular on the x-axis, the point at which the perpendicular cuts the x-axis gives us the median

**Related Articles:**