 # Decimal Expansion Of Rational Numbers

Before going into a representation of the decimal expansion of rational numbers, let us understand what rational numbers are. Any number that can be represented in the form of p/q, such that p and q are integers and q ≠ 0 are known as rational numbers. So when these numbers have been simplified further, they result in decimals. Let us learn how to expand such decimals here.

Examples:  6 , -8.1, 4/5 etc., are all examples of rational numbers. ## How to Expand Rational Numbers in Decimals?

The real numbers which are recurring or terminating in nature are generally rational numbers. For example, consider the number 33.33333……. It is a rational number as it can be represented in the form of 100/3. It can be seen that the decimal part .333…… is the non-terminating repeating part, i .e. it is a recurring decimal number.

Also the terminating decimals such as 0.375, 0.6 etc. which satisfy the condition of being rational

$$\begin{array}{l}(0.375 = \frac{3}{2^3} ,0.6 = \frac{3}{5})\end{array}$$

Consider any decimal number. For e.g. 0.567. It can be written as 567/1000 or 567/103 . Similarly, the numbers 0.6689,0.032 and .45 can be written as 6689/104, 32/103, 45/102, respectively in fractional form.

Thus, it can be seen that any decimal number can be represented as a fraction which has denominator in powers of 10. We know that prime factors of 10 are 2 and 5, it can be concluded that any decimal rational number can be easily represented in the form of p/q, such that p and q are integers and the prime factorization of q is of the form 2x5y , where x and y are non-negative integers.

This statement gives rise to a very important theorem.

### Theorems

Theorem 1: If m be any rational number whose decimal expansion is terminating in nature, then m can be expressed in form of p/q, where p and q are co-primes and the prime factorization of q is of the form 2x5y, where x and y are non-negative integers.

The converse of this theorem is also true and it can be stated as follows:

Theorem 2: If m is a rational number, which can be represented as the ratio of two integers i.e. p/q and the prime factorization of q takes the form 2x5y, where x and y are non-negative integers then, then it can be said that m has a decimal expansion which is terminating.

Consider the following examples:

1. $$\begin{array}{l}\frac{7}{8} = \frac{7}{2^3} = \frac{7\times 5^3}{2^3\times 5^3} = \frac{875}{10^3}\end{array}$$
2. $$\begin{array}{l}\frac{3}{80} = \frac{3}{2^4\times 5}= \frac{3\times 5^3}{2^4\times 5^4} = \frac{375}{10^4}\end{array}$$

Moving on, to decimal expansion of rational numbers which are recurring, the following theorem can be stated:

Theorem 3: If m is a rational number, which can be represented as the ratio of two integers i.e. p/q and the prime factorization of q does not takes the form 2x5y, where x and y are non-negative integers. Then, it can be said that m has a decimal expansion which is non-terminating repeating (recurring).

Consider the following examples:

1. $$\begin{array}{l}\frac{1}{6}= 0.1666….= 0.1\overline{6}\end{array}$$
2. $$\begin{array}{l}\frac{7}{12}= 0.58333…= 0.58\overline{3} \end{array}$$
3. $$\begin{array}{l}\frac{9}{11}= 0.8181…= 0.\overline{81}\end{array}$$

### Rational Number to decimal Examples

Case 1: Remainder equal to zero

Example: Find the decimal expansion of 3/6. Here, the quotient is 0.5 and the remainder is 0. Rational number 3/6 results in a terminating decimal.

Case 2: Remainder not equal to zero

Example: Express 5/13 in decimal form. Here, the quotient is 0.384615384 and the remainder is not zero. Notice that the number…384 after the decimal is repeating. Hence, 5/13 gives us a non-terminating recurring decimal expansion. And this can be written as

$$\begin{array}{l}5/13 = 0.\overline{384615}\end{array}$$

A rational number gives either terminating or non-terminating recurring decimal expansion. Thus, we can say that a number whose decimal expansion is terminating or non-terminating recurring is rational.

## Video Lesson on Rational Numbers 