tables with classes

Example: We ask  40 people about the number of times that they have gone to the cinema last year, and the answers are:
3, 15, 24, 28, 33, 35, 38, 42, 43, 38, 36, 34, 29, 25, 17, 7, 34, 36, 39, 44, 31, 26, 20, 11, 13, 22, 27, 47, 39, 37, 34, 32, 35, 28, 38, 41, 58, 15, 32, 13

We have several different values and then we have to group them into classes or class intervals. We choose approximately the square root of N classes and the endpoints must be round numbers.

In the table, we have to put the class mark too, which is the middle point of the interval class.