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# Why is writing in standard index form useful?

By Henry Warren on the 11th of June, 2012

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Standard form is a way of writing down very large or very small numbers easily. 10³ = 1000, so 4 × 10³ = 4000 . So 4000 can be written as 4 × 10³ . This idea can be used to write even larger numbers down easily in standard form.
Small numbers can also be written in standard form. However, instead of the index being positive (in the above example, the index was 3), it will be negative.

The rules when writing a number in standard form is that first you write down a number between 1 and 10, then you write × 10(to the power of a number).

#### Example

Write 81 900 000 000 000 in standard form:

81 900 000 000 000 = 8.19 × 1013

It’s 1013 because the decimal point has been moved 13 places to the left to get the number to be 8.19

#### Example

Write 0.000 001 2 in standard form:

0.000 001 2 = 1.2 × 10-6

It’s 10-6 because the decimal point has been moved 6 places to the right to get the number to be 1.2

On a calculator, you usually enter a number in standard form as follows:
Type in the first number (the one between 1 and 10). Press EXP . Type in the power to which the 10 is risen.

### Manipulation in Standard Form

This is best explained with an example:

#### Example

The number p written in standard form is 8 × 105
The number q written in standard form is 5 × 10-2

Multiply the two first bits of the numbers together and the two second bits together:
8 × 5 × 105 × 10-2

= 40 × 103 (Remember 105 × 10-2 = 103)

The question asks for the answer in standard form, but this is not standard form because the first part (the 40) should be a number between 1 and 10.

= 4 × 104