# Rational Numbers

Rational numbers are any numbers that can be written as a fraction. In other words, you can rewrite the number so it will have a numerator and a denominator.
They have the form
a / b
in which a and b are integers and b not equal to zero.

Notice that we said b cannot be zero. It is because any number divided by 0 has no answer.

Examples of numbers that are rational are:

 2 / 3 ,  5 / 2 , 1 / 4 ,  2, -8 / 2 ,  and 0
 2 / 3 ,  5 / 2 , 1 / 4 ,  2, -8 / 2 ,  and 0

Now, why are 2 and 0 examples of such numbers?

It is because 2 and 0 can be written as

 2 / 1 and   0 / x
 2 / 1 and   0 / x

## Decimal expansion of rational numbers

x can be any number since 0 divided by any number is zero.

We can also write rational numbers as decimals.

We do this by performing a quick division that is dividing the numerator by the denominator.

For instance,

2 / 5
= 0.4
or

2 / 5
= 0.400000000

Notice that you can continue division to keep getting zeros for the decimal places after 4. The bar on top of 0 means that if we continue to perform long division, we will keep getting an infinite number of zeros.

Another way to convert
2 / 5
into a decimal is to notice that we can multiply 5 by 20 and 2 by 20

We will get
40 / 100

And
40 / 100
= 0.40

Diving by 100 or any other power of 10 is a straightforward process.

If you are dividing by 10, just move the decimal point one place to the left.

If you are dividing by 100, just move the decimal point 2 places to the left.

and so forth...

For
40 / 100
, the decimal point is after 0 for 40.

Moving that two places to the left bring the decimal point right before the 4.

A rational number can have either repeating decimal expansion or terminating decimal expansion.

Repeating decimal expansion:

A decimal expansion in which the numbers repeat in exactly the same order.

For example, 0.251251251251 is a repeating decimal expansion because 251 keeps repeating in the same order.

Terminating decimal expansion:

A decimal expansion that ends in all zeros.

For example, 0.150 is a terminating decimal expansion.

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