Teacher2Teacher 
Q&A #7370 
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From: Loyd To: Teacher2Teacher Public Discussion Date: 2001122214:43:38 Subject: Use of Commas in Math Placing commas after every three digits is in effect putting the number in base 1000 vice base 10. This makes it very easy to read the numbers. I teach students to say thousand when the come to the comma three places from the far right. They say million when they come to the second comma and say billion when they come to the third comma. The digits of a base thousand number are 0 to 999. Here you use a group of three to express a single digit. If one wanted base ten thousand, they would place commas every four places. This idea when extended to base 16 makes it easy to convert from hexadecimal to octal and then to binary. Computer programmers usually are aware of this fact. Placing commas every three places in a binary number converts it to octal expressed with binary digits, that is, 0 & 1. From there, one can write the octal number using digits 1 to 7. Maybe you have noticed that 1000 in base two is equivalent to 8 or 2 raised to the 3 power. In the same way 1000 in base 10 is 10 raised to the third power. I believe it is important for the teacher require the students to use commas as it helps to read the number or numeral.
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