There are so many things around us that go unnoticed that shields a logic to itself. One such thing is number of blades in a fan.
Fans come with both 3 and 4 blades depending on the place where they are being used. In India, we usually have them with 3 blades. But the one's with 4 blades, which are mostly used in the US and colder areas, are not just designed that way to look different. There's a reason behind it.
In US, the sole aim of a ceiling fan is to supplement the air conditioner. Which is why the fan, which is slower than the one with 3 blades, serves the purpose of keeping air circulation in the room.
The 4 blades move a large mass of air. While In India, owing to the economical aspect, many families use fans as the only source of cooling. The 3-blade fan is lighter and operate at greater strength and is also energy efficient.