Things that happen around us can be majorly divided into 2 categories. One - that happen without any rhyme or reason, and two - that do have a reason but we never really got down to think about it. One such thing is the number of blades of a fan.
Now you might have noticed, 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.