Place Value and the Number NineDate: 08/31/2002 at 18:53:12 From: Jacque L. Sievers Subject: The number nine - place value I am asking this for my 10-year-old grandson. Why is 9 the largest number you can put into any place value spot? Date: 08/31/2002 at 23:21:02 From: Doctor Peterson Subject: Re: The number nine - place value Hi, Jacques. The base-ten system is built around the idea that you can name every number by counting tens. Once you have ten tens, you give it a new name (hundreds) and write it using the hundreds place. When you get ten hundreds, you give that a new name (thousands) and use the thousands place. You never need to write a digit larger than 9, because ten of anything gets a new name. Suppose we did use ten as a digit. We could talk about the number "tenty," meaning ten tens, and write it perhaps as X0, using X as the symbol for the digit ten. That would really be the same as one hundred; since we already have a name for it, it would be redundant. So we don't need an extra symbol for ten; X is written as 10, and X0 as 100. But occasionally you will see such ideas used humorously. In _The Lord of the Rings_, the story begins with Bilbo Baggins' "eleventy-first birthday." That would mean eleven tens and one, or 110+1, which is really 111. Again, we have a way to say it without using "eleventy," so we don't need to use eleven as a digit. If you have any further questions, feel free to write back. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/ |
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