# 0123456789   Arabic Numerals   9876543210

Arabic Numbers --- Introduction --- Add --- Subtract --- Multiply --- Divide --- Practise sums --- Less than 1 --- Types of numbers

### Count with Arabic numbers

Here is a simple counter. You can change the start number, or what the step is. If you start from zero, you can use the step number to go through a Times Table.

 Start number: every

### How to write Arabic digits

You may think that it's obvious how you write the digits of Arabic numbers: 0 1 2 3 4 5 6 7 8 9. But this is how they are printed. There are different writen versions, such as (instead of 4), (instead of 9) and (instead of 1). In mainland Europe, they can write 1 in a more exagerrated form as . This can be confused with 7, so they cross their sevens like this . They write their decimal points in a different way as well. In computing, numbers and letters are often mixed together, and it is important to get them right. Decades ago, programmers and other computer people wouldn't enter data into the computer directly. They wrote it down, and data entry clerks would type this onto punched cards or tape. Zero and the letter "O" can be confused, so computer people would write the letter as O and slash their zeroes as . Some people used the opposite convention! Also the slashed O is a Scandinavian letter. The letter I and the number one can get muddled as well, so computer people would write them in a seriffed form as 1 and . Sometimes one was written as .

Modern typwriters have the digit for zero after the digit for nine, on the top row. There is often a number pad on the right of the keyboard. The old manual typewriters had as few keys as possible, as each key needed a metal hinged bar to strike the paper to type the letter. So there was no one and no zero. You had to type a capital letter "O" for zero, and a lower case letter "L" for one.

### How Arabic numbers worked

The Arabic numeral system is very clever. Most of the number systems of ancient cultures, such as the Egyptians, Greeks or Romans, relied on finding more symbols as the numbers got and bigger. For very big numbers, either the symbols became clumsy or people had different versions. It could also hard to instantly see exactly what a number was. Finally, arithmetic was difficult.

The Arabic numbers only have ten symbols, which are the digits from zero to nine. For all bigger numbers, you know what the digit means by where it is in the number. So 2495 means 2 thousand, 4 hundred, 9 tens and 5 units. This is called a positional system. The Arabic numbers also have a zero which is important. For example, you may need to say that you have nothing in the tens column. If you left a space, then someone might read it long, and anyway, it would be hard to tell the difference between 201 and 2001.

Look at the small green squares below. It is very hard to count them. If you have to count a large number of things, it is much easier if they are grouped into collections of thousands, hundreds, tens and ones. Click on Group blocks to make them easier to count.

Enter number of squares:

### Visualise a million

The exercise above gives you an idea of numbers in their thousands. Here is a way to imagine how big a million is. This cube has a hundred tiny squares on each side. That means that it contains 100x100x100 or a million squares in all. I am sorry that the perspective looks wrong, but it's rather hard enough to draw a million squares!

You can imagine larger numbers as well. A cube with sides of one metre contains one billion millimetres. So a thousand of these cubes (which would take up quite a bit of space!) would contain a trillion millimetres.

If you found the cube difficult to see, here are a million dots laid out on the screen. I'm afraid that you'll need to scroll right a little, and scroll down a lot. They change colour every 100,000.