For the non-overlapping classes 0—19 , 20—39 , 40—59 the class mark of the class 0—19 is(a) 0(b) 19(c) 9.5(d) none of these

Break Down the Problem

1. Identify the given classes and their ranges:
   • Class 1: 0—19
   • Class 2: 20—39
   • Class 3: 40—59
2. Understand the concept of class mark (midpoint) for a class interval.

Relevant Concepts

The class mark (also known as the midpoint) of a class interval is calculated using the formula: $\text{Class Mark} = \frac{\text{Lower Limit} + \text{Upper Limit}}{2}$ For the class 0—19:

• Lower Limit = 0
• Upper Limit = 19

Analysis and Detail

1. Substitute the limits into the formula: $\text{Class Mark} = \frac{0 + 19}{2} = \frac{19}{2} = 9.5$

Verify and Summarize

The calculated class mark for the class interval 0—19 is 9.5.

Final Answer

The class mark of the class 0—19 is (c) 9.5.