Why did the egyptians make a numeral system based on ten?

The Egyptians had a writing system based on hieroglyphs from around 3000 BC. Hieroglyphs are little pictures representing words. It is easy to see how they would denote the word "bird" by a little picture of a bird but clearly without further development this system of writing cannot represent many words. The way round this problem adopted by the ancient Egyptians was to use the spoken sounds of words. For example, to illustrate the idea with an English sentence, we can see how "I hear a barking dog" might be represented by:

"an eye", "an ear", "bark of tree" + "head with crown", "a dog".

Of course the same symbols might mean something different in a different context, so "an eye" might mean "see" while "an ear" might signify "sound".

The Egyptians had a bases 10 system of hieroglyphs for numerals. By this we mean that they has separate symbols for one unit, one ten, one hundred, one thousand, one ten thousand, one hundred thousand, and one million

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