The speed limit should be obeyed regardless of the actions of others.  Don't follow (what amounts to) the peer pressure of other cars.

Round. Relatively small. Less than 1 inch in diameter.

It can be more specific in terms of the number of significant figures in a number.

There are several ways You could multiply to get a common denominator: 6/4 and 6/5 = 30/20 and 24/20 You could use a calculator: 6/4 and 6/5 = 1.5 and 1.2