Answer :

To determine the class mark (midpoint) of the interval, we follow these steps:

1. Identify the lower and upper limits of the interval. Here, the lower limit is [tex]$25$[/tex] and the upper limit is [tex]$35$[/tex].

2. The class mark is calculated as the midpoint of the interval using the formula:
[tex]$$
\text{Class mark} = \frac{\text{lower limit} + \text{upper limit}}{2}
$$[/tex]

3. Substitute the values into the formula:
[tex]$$
\text{Class mark} = \frac{25 + 35}{2}
$$[/tex]

4. Perform the addition inside the numerator:
[tex]$$
25 + 35 = 60
$$[/tex]

5. Finally, divide by [tex]$2$[/tex]:
[tex]$$
\text{Class mark} = \frac{60}{2} = 30
$$[/tex]

Thus, the class mark of the interval [tex]$25-35$[/tex] is [tex]$30$[/tex]. Therefore, the correct answer is option 4.

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