__6.1 Class Interval__**1.**Data that consist of the measurement of a quantity can be grouped into few

**classes**and the

**range**of each class in known as the

**class interval**.

**(A) Class Limits and Boundaries**

**Lower Limit and Upper Limit**

**2.**For class interval, for example 30 – 39, the

**smaller value**(30) is known as the

**lower limit**while the

**larger value**(39) is known as the

**upper limit**.

**Lower Boundary and Upper Boundary**

**3.**The

**lower boundary**of a class interval is the

**middle value**between the

**lower limit**of the class interval and the

**upper limit**of the class before it.

**4.**The

**upper boundary**of a class interval is the

**middle value**between the

**upper limit**of the class interval and the

**lower limit**of the class after it.

**Example:**

20 – 29 |
30 – 39 |
40 – 49 |

$\begin{array}{l}\text{Lower boundary of the class}30-39\\ =\frac{29+30}{2}=29.5\\ \\ \text{Upper boundary of the class}30-39\\ =\frac{39+40}{2}=39.5\end{array}$

**(B) Class size**

**5.**The

**class size**is the

**difference**between the

**upper boundary**and the

**lower boundary**of the class.

**Example:**

Size of class interval 30 – 39

= Upper boundary – Lower boundary

= 39.5 – 29.5

= 10