According to the meaning of the question, the canteen is divided into three kinds of dishes. The topic covers all the combinations of one dish and two dishes, and points out the number of people who like to eat.

In this case, the class size should be here, and I don't think there should be people waiting for death without eating.

The problem now is: the number of people who love two kinds of dishes includes the number of people who love one kind of dish, and there is double counting; Similarly, the number of people who love to eat three kinds of dishes also includes the number of people who love to eat two kinds of dishes, and there is also double counting.

So the class size should be equal to the number of people who like to eat one dish minus the difference between the number of people who like to eat two dishes and the number of people who like to eat three dishes.

So, the number of people who love to eat these three foods is:

Class size-(number of people who like one dish-number of people who like two dishes)

=50-[(40+32+40)-(28+22+30)]

=50-[ 1 12-80]

=50-32

= 18 (person)

The corresponding schematic diagram is as follows: