Within the same first three IPv4 numbers, /24 has 256 addresses, /25 has 128 and /26 has 64. A /26 block starts at last number 0, 64, 128 or 192. In these ordinary networks, the first address names the network and the last is broadcast. Do not assign either to a host or reuse an occupied address. Special /31 and /32 cases are outside this exercise.
Worked example
Separate example: 192.0.2.0/25 covers last numbers 0-127. Hosts are 1-126, giving 126 host addresses before counting any already in use.
Workshop D / fictional address inventory
All addresses begin with 192.0.2. Workshop D uses /26 and must contain a new laptop ending in 242. Currently the gateway uses 193, a printer uses 208, a server uses 221 and a tablet uses 250. These are the only four occupied addresses; the new laptop has not been assigned yet. Use only this paper inventory. Do not configure or contact real devices. For numeric questions, enter just the last number.