[[1]] is the class mark of a class a-b?

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Detailed Solution

Here we were given the interval a-b and asked to determine the value of the class marks. But first, we'll learn about class grades and class limits.
The class mark is defined as the average value or the middle value of a given interval in the frequency distribution. Class marks are also called class centers. In other words, we can say that the class marks are the average of the upper class and the lower class. So let's see what the class limits are.
When we talk about class limits, they are of two types namely lower class limit and higher class limit. The lower class limit indicates the minimum value of data that can be included in an interval, while the upper class limit indicates the maximum value of data that can be entered in that interval. We use formulas to find these two types of class limits
Lower class limit = class mark -

\frac{class size}{2}

Upper class limit = class mark +

\frac{class size}{2}

The above formulas are used when we have not been provided with intervals. But in the given question, we have been provided with an interval a-b. So, we have
⇒ class mark =