A number system based on the number 10; the number system in common use. All rational numbers can be written as a finite decimal (e.g. 1/4 = 0.25) or a repeating decimal (e.g. 5/27 = 0.185 185 185…). An irrational number can be written to any number of decimal places, but can never be given exactly (e.g. √3 = 1.732 050 8…).