"How many hosts are there in a /23 network?"

Having interviewed a lot of sysadmins, I see this trip people up, mostly because the slash/bits network notation isn't taught/documented well. The "memorize a table" approach seems to be common.

Most of them, with a bit of prompting, get that an ipv4 is 32 bits, and that a /23 means (32-23==9) 9 bits of host addresses. Most also can figure out what 111111111 is. Some remember to account for the network and broadcast address not being available for hosts.