Calculation of PDV for FE, how to count switches?

Question

System administration

Tell me how to correctly calculate PDV for FastEthernet in the presence of switches.
For example PC1-> 20m -> Switch -> 20m -> Switch -> PC2
Level 2 switches.
There are no hubs.
CAT 5e 1.112bt cable

Answer 1

how to count switches?

No way. PDV makes sense within a single collision domain, and switches divide the network into different collision domains.
In your example, there will be three domains, within each of them PDV = 2 * 20 * 1.112.