There are many things that come in groups of 45. Because 45 is a round number since it ends in 5, there are many things that have 45 objects in them. If you drive a car, you may notice that many roads and streets have signs posted for speed limits. Forty-five mile per hour signs are common because they want people to drive below that speed limit. Also, in math, many times you will see in geometry 45-degree angles in triangle. That is a common angle amount. Finally, 45 days is a common amount of time to use for something. It is a month and a half. If you ever have bought a house, at first it was expected for buyers to close on a house within 30 days. However, now it takes longer and it could be about 45 days.