Find the width of the class 35-45?

Hint: We first explain the difference between class limits and class boundaries. Then we take the difference of the end-points of the class boundaries to find the class width. The difference is usually the subtraction of the lower end from the upper end.

Complete step-by-step solution:
The class width can be determined from the difference of the end-points of the class boundaries.
For each class we have two class limits. They are called upper class limits and lower-class limits. We convert them to class boundaries which are halfway points that separate the classes. The lower-class boundary of a given class is obtained by averaging the upper limit of the previous class and the lower limit of the given class. The upper-class boundary of a given class is obtained by averaging the upper limit of the class and the lower limit of the next class.
If for a particular class, the end points are ${{x}_{l}},{{x}_{u}}$, then the class width is ${{x}_{u}}-{{x}_{l}}$.
For the given class 35-45, the class width will be $45-35=10$.

Note: Through in a grouped data the class intervals can be of unequal size, usually we will meet class intervals of equal size. In case of non overlapping intervals, the gaps between consecutive intervals may be unequal. But at this level we will deal with intervals with equal gaps between consecutive classes.