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Last modified on January 13th, 2022

Rational numbers are a segment of the real numbers, which can be written in p/q form where p and q are an integer and q (the denominator) is not equal to zero. Rational numbers originated from the concept of ratio.

Given below are some examples of rational numbers:

- 1/2 or 0.5
- -6/7
- -0.25 or -1/4
- -13/15 or -0.8666666666666667

The rational numbers are universally represented by the symbol ‘Q’.

Rational numbers are closed under addition, subtraction, multiplication, and division operations.

In simple words, addition, subtraction, multiplication, and division of 2 rational numbers ‘a’ and ‘b’ give a rational number. In rational numbers (p/q form), q ≠ 0. If q = 0, the result is undefined.

For example:

- 6/7 + 2/9 = 68/63
- 3/5 – 1/7 = 16/35
- 2/3 × 3/9 = 2/9
- 7/15 ÷ 10/3 = 7/50

Rational numbers are commutative under the operations – addition and multiplication. However, this property does not hold for subtraction or division of 2 rational numbers.

⇒ a + b = b + a, here a and b are 2 rational numbers

And, a × b = b × a

⇒ a – b ≠ b – a,

And, a ÷ b ≠ b ÷ a

For example:

- 1/3 + 2/3 = 2/3 + 1/3

= 3/3 = 1

- 7/8 × 8/9 = 8/9 × 7/8

= 7/9

Rational numbers have the associative property for only addition and multiplication.

For example:

⇒ a + (b + c) = (a + b) + c, here a and b are 2 rational numbers

And, a × (b × c) = (a × b) × c

- 1/3 + (1/5 + 2/4) = (1/3 + 1/5) + 2/4

= 31/30

- 3/7 × (2/5 × 3/4) = (3/7 × 2/5) × 3/4

= 9/70

According to this property, the multiplication of a whole number is distributed over the sum of the whole numbers.

⇒ a × (b + c) = (a × b) + (a × c), here a and b are 2 rational numbers

For example:

- 1/3 x (1/6 + 1/7) = (1/3 x 1/6) + (1/3 x 1/7)

= 13/126

According to Identity property, 0 is an additive identity and 1 is a multiplicative identity for rational numbers.

⇒ a/b + 0 = a/b (Additive Identity)

a/b x 1 = a/b (Multiplicative Identity)

For example:

- 3/4 + 0 = 3/4 (Additive Identity)
- 3/4 x 1 = 3/4 (Multiplicative Identity)

According to Identity property, for a rational number a/b, its additive inverse is -a/y, and b/a is its multiplicative inverse.

⇒ a/b + (-a/b) = 0 , here the additive inverse of a/b = (-a/b)

And, a/b x b/a = 1, here the multiplicative inverse a/b = b/a

For example:

- 2/9 + (-2/9) = 0, here the additive inverse of 2/9 is -2/9
- 3/8 x 8/3 = 1, here the multiplicative inverse of 3/8 is 8/3.

We need to check the following conditions to identify a rational number.

- It is written as p/q, where q ≠ 0.
- The ratio p/q can be simplified further and written in decimal form

Rational numbers:

- Consist of positive, negative numbers, and zero
- It can be written as a fraction

For example:

Is 0.3505350535053505… a rational number?

The number above has a set of decimals 3505, which is repeated continuously here.

We must not consider any fraction with integers as rational numbers. Below are the different types of rational numbers:

- integers like -1, 0, 3 etc.
- fractions with numerators and denominators are integers such as 2/5, -6/7

(example: 12/45 is not a rational number as it can be further simplified into the standard form as 4/15. So the rational number here is 4/15)

In simple words, rational numbers are of 2 types:

**Standard**– a fraction that cannot be simplified further but can be written in decimal form**Positive and negative rational numbers**

Positive Rational Numbers | Negative Rational Numbers |

Both numerator and denominator have the same signs. | numerator and denominator have the different signs. |

greater than 0 (p/q > 0) E.g. 2/5, 4/9 | less than 0 (p/q < 0) E.g. 2/-9, -5/8 |

So **are decimals rational numbers**?

Rational numbers can be decimals with

**terminating decimals**such as 1/8 (0.125), 1/16 (0.0625), or**non-terminating decimals**with repeating patterns (after the decimal point) such as 1/15 (0.0666666666666667), 2/9 (0.2222222222222222).

So **are all integers rational numbers**?

Yes. Any integer is a rational number. It can be expressed as a fraction or terminating decimal using the properties of rational numbers.

We add and subtract rational numbers in the same way we do with fractions. While adding or subtracting any 2 rational numbers, we make their denominators equal and add the numerators.

For example:

2/3 – (-3/5)= 2/3 + 3/5 = 2/3 × 5/5 + 3/5 × 3/3 = 10/15 + 9/15 = 19/15

We multiply and divide rational numbers in the same way we do with fractions. While multiplying or dividing any 2 rational numbers, we multiply the numerators and the denominators separately. Then we simplify the result.

For example:

1/2 × -2/5 = (1 × -2)/(2 × 5)= -2/10

While dividing any 2 fractions, we convert any one of the fractions into their own reciprocal and then multiply with the other.

For example:

5/7 ÷ 9/28 = 5/7 × 28/9 = 20/9 = ${2\dfrac{2}{9}}$

From the discussion above, it is evident that the range of rational numbers is infinite. So we do not have a list of rational numbers. Hence, we cannot find the smallest rational number.

So **is 0 a rational number**?

Yes. As we know, a number written in p/q form where q ≠ 0, 0 can also be written in p/q form such as 0/1, 0/2, 0/3, 0/-4, 0/5/0.8.

The numbers which are not rational are considered irrational. We will learn about the differences in the next article.

**[**link **Difference Between Rational and Irrational Numbers** article here**]**

**Find the rational numbers in the following set – √3/2, 3/7, – 5/8, π, 1.512362309…..**

Solution:

As we know,

Simplifying a rational number gives terminating or a non-terminating decimal with repeating pattern

∴ the rational numbers in the following set is 3/7 and – 5/8

**Find a rational number among the following- 1/3 and 2/5.**

Solution:

As we know,

The average of any 2 numbers is attained from the 2 given numbers.

(1/3 + 2/5) ÷ 2

= 11/15 × 1/2

= 11/30

**Ans. **Rational numbers consist of all positive and negative numbers and zero. The numbers can be written as p/q form with the signs. These include Whole numbers, integers, fractions, terminating, and repeating decimals.

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Last modified on January 13th, 2022