Question 19

Explanation

The student visitation data forms a number sequence: $7, 10, 12, 15, 17, 20$. We will analyze the difference between terms to find the pattern.

It appears that the addition pattern alternates between $+3$ and $+2$. Since the last term ($20$) was obtained by adding $+3$, the next step to find the 7th day is to add $+2$.

Thus, the number of students visiting on the 7th day is predicted to be $22$ people.