A speaker system is plugged into a 100v socket and 2.5 a of current runs through. Find the power of the system

No need for complicated calculations of total speaker impedance - simply add together each speaker's wattage (see below for more details)

Many speakers can be connected to an amplifier.

Extra speakers can normally be added to the system

The volume of each speaker can be adjusted independent of the main volume (so the toilet speakers are not as loud as the foyer speakers).

Smaller cables can be used. Distributed speaker systems use much less current through the speaker cables

Longer speaker cables are possible with minimal line loss. Cables runs can be 100's of metres or 1000's of feet.