For example, 123.456 represents 123456⁄1000, or, in words,

*one*hundred, two tens, three*ones*,*four*tenths, five hundredths, and six thousandths. A real number can be expressed by a finite number of decimal digits only if it is rational and its fractional part has a denominator whose prime factors are 2 or 5 or both, because these are the prime factors of 10, the base of the decimal system. Thus, for example,*one*half is 0.5,*one*fifth is 0.2,*one*-tenth is 0.1, and*one*fiftieth is 0.02. Representing other real numbers as decimals would require an infinite sequence of digits to the right of the decimal point.