The class marks of a frequency distribution are 104, 114, 124, 134, 144, 154, and 164. Find the class size.

The class mark is defined as the mid-value of each class interval.

Class marks are 104, 114, 124, 134, 144, 154, and 164.

Class size is the difference between the upper limit and lower limit of a class interval.

Since the class marks are equally spaced, then the class size = (114 - 104) = 10

Therefore, the class size must be 10.