Today we mostly use Arabic numerals, such as 1, 2 and 3, which we join together to make numbers like 123. The Romans had the start of a system where position was important, but with Arabic numbers every position is important. The individual numerals are called digits. This comes from the Latin digitus, meaning finger, and tells us how counting was done originally.

The decimal system is fairly easy. The units count single items. 1 = one, 2 = two and so on. But then in the next position everything is multiplied by ten. 10 = ten, 20 = twenty and so on. In the third position along from the right, we multiply by ten again, which means that this position is for hundreds (ten times ten equals a hundred). And the next position is for thousands, and then for tens of thousands, and so on. As big as you like!

The 0 (zero) is an important idea that we got from the Arabs, along with the whole Arabic numeral thing. Before it, we had no way to write zero. Zero wasn’t even thought of as a number. There’s no way to write zero in Roman numerals. That brings me back to Roman numerals, and the answer to yesterday’s question. MCMXCIX is 1999 in decimal. Did you get it?

That sums it up.

## Monday, 23 February 2009

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