How many of cable links required for the following given network topology?

(ii) For 5 devices with bus topology

I fond 2 answer can you explane why some of them say n-1 and other sad n+1

5 + 1 (n mean cables, 1 mean backbone) 5+1= 6 links

https://www.chegg.com/homework-help/questions-and-answers/210-computer-network-question-two-many-cable-links-required-following-given-network-topolo-q26602070?trackid=787067d6&strackid=4a641293&ii=4

For n devices in a network, what is the number of cable links required for a mesh, ring, bus, and star topology?

The number of cable links required by each network topology are given below. n is the number of devices in the network. Mesh: n * (n-1) / 2

Ring: n

Bus: n + 1 (n for cables, 1 for backbone)

Star: n

http://www.thedailyprogrammer.com/2015/10/data-communications-and-networking.html

thank you