Kobanava Xiaohei took part in the math competition, and the number of Xiaohua was No.8.

The serial number that Xiaohei caught was 19. Ask Kobanawa how many people are separated from Blackie.

19-8- 1= 10

There are 10 people separated by Xiaohei in Kobanawa.

Note that if you subtract 1, such as serial numbers 8 and 9, there is no interval.