ANSWERS: 5

Base ten as you know is 19 plus 0. It is a common "human" counting method. Some sciene applications use base 11, base 16, blah. Reserved for complex maths and "fun" for the eggheads. Other than base ten the most popular and most widespread method of 'counting' is base 2. It is called binary and is 0 and 1.

Hm. I'm thinking Roman Numerals. They sort of counted with a base of three, didn't they?

I've never heard of any stillactive culture which uses anything other than base 10 for normal operations. Obviously in computers base 2, base 8, and base 16 are popular. It seems to me I've heard that the Babylonians and Mayans both used odd bases (12? 36?).

Binary arithmetic is used in computers, and the hexadecimal (base 16) system is used a lot by people who work with computers. On the other hand there are some languages such as Pirahã, a language from the Amazon basin (see http://en.wikipedia.org/wiki/Pirah%C3%A3_language) which don't have words for all the numbers we have. In fact it's not clear if Pirahã has any numbers at all.

The number system we use today was dicovered by an Indian mathematician known as Aryabhatta and then spread to Europe thru Arabs. This number system was used to be known as Arabic but now it is called Hindu Arabic or Indian numbers. It was Brahmagupta who developed multiplication and division using Hindu number system. Where can I find a photo of him?
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