Number of two ends: number = difference+1.

Not counting both ends: number = difference-1.

There is only one head: Quantity = Difference

Question: How many people are there between 1: 13 and 19? Obviously, both ends are not counted, so the median number = difference-1= (19-13)-1= 5 people.

Question 2: 1 1 and 18 pages are counted in the number of pages read, and the number of pages read = difference+1= (18-1)+1.

Question 3: You can imitate the question 1 and use the number between the number 15 and the number 8, or you can not use this rule. Numbers in the box = total number-front number-back number, 15-8- 1=6.