Rational Numbers

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The idea of rational numbers is a major step in abstraction in thinking about numbers. It moves from thinking about numbers as representing concrete physical situations to numbers as entities which can be operated on without any reference necessarily to physical concrete situations.

Rational number is any number which can be written in the form a/b, where a &amp; b are integers (numbers like -2) and b is not equal to 0. It is better if a &amp; b are relatively prime.

Some life situations could be related to the idea of rational numbers, like comparing parts of a whole to the whole. But essentially, they are thought of as abstract entities which can be operated on as per certain rules accepted by all mathematicians.

The name &lsquo;rational&rsquo; here indicates that the idea emerged from ratios which are numbers of the type a/b, where a &amp; b are positive numbers. In a rational numbers they can be integers.

The rules of operating on rational numbers are worked out such that they follow the laws of Arithmetic. Any entity which obeys these laws is considered as a number.

Rational Numbers imply just the form in which the number is written. They lend themselves to multiple interpretations, of which idea fractions is just one.

Fraction- A fraction can be thought of a whole being divided into 8 equal parts out of which 5 are taken. This can be called the Part-Whole relation.

Ratio- Another is the Ratio idea – as can be thought of as a ratio of a &amp; b. The ratio idea is not a number in the sense we have studied in primary classes. It is more like a relation between a &amp; b. This relation, as we shall see in Section 18 on ratios, is qualitatively different from the relation between a &amp; b in a fraction of the same form.

Division fact-Another is the division idea where a/b represents the division of a by b. Numerically this leads to the same result. Dividing 1 pizza into 4 equal parts and taking 3 out of them leads to the same quantity as taking 3 pizzas and dividing them into 4 equal parts.

Measure- Another idea is that a rational number can be marked on a number line much like whole numbers. In that way it gives a measure of the number. A number like will be located between 0 and 1. A number like will be located between 1 &amp; 2. A number like will be located between 0 and -1.

Decimal- As an extension of the Measure idea, rational numbers can also be thought of as decimals. The decimal representation of rational &amp; other numbers, brought out their differences very clearly and led to the idea of the set of real numbers.

The idea of rational numbers covers all the numbers we have studied until now (whole numbers &amp; fractions) as well as numbers we would shortly be studying (decimal fractions &amp; integers). It also sets the stage for learning about irrational numbers, which we would study in chapter 17.10.

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