Why do fans (and propellers) have different numbers of blades? What advantage is there to more or less blades?

Question

An actual question my five year old asked me and I couldn’t answer, please help!

In: Physics

Answer 1

Moving lots of blades is hard, so only 2 blades is the best. But, if you can’t make them big and strong enough, then you have to put more blades on the propeller.