Let's look at numbers with the same digit in different places and see if we can determine some relationship.
Consider the number 20.
Now, consider the number 200, which has the 2 in the location just to the left of where it is in 20. You're expect to observe that the number 200 is ten times the number 20.
Consider the number with the 2 in the position to the right of where it is in 20. That number is 2. You are expected to observe that the number 2 is one-tenth the number 20.
The place-value of a digit increases by a factor of 10 when moved one place left, and is reduced by a factor of 1/10 when moved one place right.
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This is what makes a place-value number system work. In Roman Numerals, for example, the value of a character is changed by ...
- putting it ahead of or after a higher-value character: IV, VI
- changing the character: I, V, X, L, C, D, M
Place-value number systems don't have to have 10 as their base. We use 60 for the base in (minutes):(seconds), both for time and angle measures. We use 2, 8, or 16 as the base in the binary, octal, and hexadecimal numbers used by computer systems. These other place-value systems have the same characteristic: the value of a digit is increased by a factor of the base when moved to the left, and decreased by a factor of the base when moved to the right. (The hexadecimal value A7C0 has 16 times the value of A7C, for example, and 1/16th the value of A7C00.)