Fraction in mathematics call the rational number equal to one or several shares into which unit is divided. At the same time record of fraction has to contain the instruction on two numbers: one of them specifies into how many shares unit was broken during creation of this fraction, and another - how many from these shares includes fractional number. If these two numbers register in the form of the divided line of numerator and a denominator, then call such format "ordinary" fraction. However there is also other format of fractions called "decimal".
The three-storyed form of record of numbers in which the denominator is located over numerator and between them is also dividing line, is not always convenient. Especially this inconvenience began to be shown with mass distribution of personal computers. The decimal form of representation of fractions is deprived of this shortcoming - it is not required to specify numerator as it by definition is always equal to ten in negative degree in it. Therefore the fractional number can be written down in one line though its length in most cases will be much more, than length of the corresponding common fraction.
Other advantage of record of numbers in a format of decimal fraction is that it is much simpler to compare them among themselves. As the denominator of each category of two such numbers is identical, it is enough to compare only two figures of the corresponding categories while when comparing common fractions it is necessary to take into account and numerator, and a denominator of each of them. This advantage is important not only for people, but also for computers - it is rather easy to program comparison of numbers in a decimal format.
There are rules of addition, multiplication and other mathematical operations developed centuries which allow on paper or in mind to make calculations with numbers in a format of decimal fractions. In it one more advantage of this format before common fractions is concluded. Though with development of computer technologies when the calculator is even in hours, it becomes less noticeable. The described pluses of a decimal format of fractional numbers show that its basic purpose - simplification of work with mathematical sizes. Such format has shortcomings too - for example to write down periodic fractions to decimal fraction it is necessary to add also number in brackets, and irrational numbers in a decimal format always have approximate value. However at today's level of development of people and their technologies it is much more convenient in use, than an ordinary format of fractions.