131. You will here naturally ask, What is the use of decimal fractions, if the greater number of fractions cannot be reduced at all to decimals? The answer is this: The addition, subtraction, multiplication, and division of decimal fractions are much easier than those of common fractions; and though we cannot reduce all common fractions to decimals, yet we can find decimal fractions so near to each of them, that the error arising from using the decimal instead of the common fraction will not be perceptible. For example, if we suppose an inch to be divided into ten million of equal parts, one of those parts by itself will not be visible to the eye. Therefore, in finding a length, an error of a ten-millionth part of an inch is of no consequence, even where the finest measurement is necessary. Now, by carrying on the table in (129), we shall see that
| 1428571 | does not differ from | 1 | by | 1 | ; |
| 10000000 | 7 | 10000000 |
and if these fractions represented parts of an inch, the first might be used for the second, since the difference is not perceptible. In applying arithmetic to practice, nothing can be measured so accurately as to be represented in numbers without any error whatever, whether it be length, weight, or any other species of magnitude. It is therefore unnecessary to use any other than decimal fractions, since, by means of them, any quantity may be represented with as much correctness as by any other method.
EXERCISES.
Find decimal fractions which do not differ from the following fractions by ¹/₁₀₀₀₀₀₀₀₀.
| ⅓ | Answer, | ³³³³³³³³/₁₀₀₀₀₀₀₀₀. |
| ⁴/₇ | ⁵⁷¹⁴²⁸⁵⁷/₁₀₀₀₀₀₀₀₀. | |
| ¹¹³/₃₅₅ | ³¹⁸³⁰⁹⁸⁵/₁₀₀₀₀₀₀₀₀. | |
| ³⁵⁵/₁₁₃ | ³¹⁴¹⁵⁹²⁹²/₁₀₀₀₀₀₀₀₀. |
132. Every decimal may be immediately reduced to a quantity consisting either of a whole number and more simple decimals, or of more simple decimals alone, having one figure only in each of the numerators. Take, for example,
| 147326 | . By (115) | 147326 | is 147 | 326 | ; |
| 1000 | 1000 | 1000 |
and since 326 is made up of 300, and 20, and 6; by (112) ³²⁶/₁₀₀₀₀ = ³⁰⁰/₁₀₀₀ + ²⁰/₁₀₀₀ + ⁶/₁₀₀₀. But (108) ³⁰⁰/₁₀₀₀ is ³/₁₀, and ²⁰/₁₀₀₀ is ²/₁₀₀. Therefore, ¹¹⁴⁷³²6/₁₀₀₀ is made up of 147 + ³/₁₀ + ²/₁₀₀ + 6/₁₀₀₀. Now, take any number, for example, 147326, and form a number of fractions having for their numerators this number, and for their denominators 1, 10, 100, 1000, 10000, &c., and reduce these fractions into numbers and more simple decimals, in the foregoing manner, which will give the table below.
DECOMPOSITION OF A DECIMAL FRACTION.