Question

The class mark of a particular class is $17.5$ and the class size is $5$. The class interval is:

• A. $14-19$
• B. $15-20$
• C. $14.5-19.5$
• D. $17.5-22.5$

Answer 1

The correct option is B $15-20$

Class mark $=\frac{\text{lower limit}+\text{upper limit}}{2}$
Thus, lower limit $+$ upper limit $=35$ ....(1)
and Class interval $=$ upper limit $-$ lower limit
Thus, upper limit $-$ lower limit $=5$ .....(2)
Adding (1) and (2), we get
$2$ (upper limit) $=40$

Upper limit $=20$
Hence, lower limit $=15$
Thus, class interval is $15-20$.