The system of fractions expressed by the use
of the decimal point, that is, fractions in
which the denominator is any higher power of
10. Thus 3/10, 51/100, 23/1,000 are decimal
fractions and are normally expressed as 0.3,
0.51, 0.023. The use of decimals greatly
simplifies addition and multiplication of
fractions, though not all fractions can be
expressed exactly as decimal fractions. The
regular use of the decimal point appears to
have been introduced about 1585, but the
occasional use of decimal fractions can be
traced back as far as the 12th century.