The calculation is as follows:

Let the day when Xiao Zhang turns over the calendar be X, then the sum of the values of these seven days is:

x+(x- 1)+(x-2)+(x-3)+(x-4)+(x-5)+(x-6)= 77

De: 7x-2 1=77

x=(77+2 1)/7= 14

So, this day is 14.

The relationship between data and operators

1) natural data representation. For example, find the area of a curved trapezoid;

2) Manual data processing (such as data in the program;

3) Manual processing of natural data. For example, a part of an image is enlarged.

In mathematical formulas, data and operators have specific and detailed relationships, such as data number, left and right functions, formula form and so on.