##### Unicode Entity and Decimal Value

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### Roman Numerals

##### Introduction

- The decimal number system, also called the Arabic number system, is a positional number system in which the position of the digit determines its value. The 2 in 521 represents 20, but the 2 in 245 represents 200.

- The Roman numeral system is an additive and subtractive system in which the value of a numeral remains constant. The C in CXX represents a value of 100, just as the C in CLXV represents 100.

 Roman Numeral Value SS 1/2 I 1 V 5 X 10 L 50 C 100 D 500 M 1000

 1 ⇝ I 10 ⇝ X 100 ⇝ C 1000 ⇝ M 2 ⇝ II 20 ⇝ XX 200 ⇝ CC 2000 ⇝ MM 3 ⇝ III 30 ⇝ XXX 300 ⇝ CCC 3000 ⇝ MMM 4 ⇝ IV 40 ⇝ XL 400 ⇝ CD 5 ⇝ V 50 ⇝ L 500 ⇝ D 6 ⇝ VI 60 ⇝ LX 600 ⇝ DC 7 ⇝ VII 70 ⇝ LXX 700 ⇝ DCC 8 ⇝ VIII 80 ⇝ LXXX 800 ⇝ DCCC 9 ⇝ IX 90 ⇝ XC 900 ⇝ CM 1/2 ⇝ SS

###### Rules for Forming Roman Numerals
1. Start from the left with the largest numeral and work down to the smallest on the right.
2. No more than three of the same numeral in a row. 40 cannot be written XXXX.
3. If a smaller numeral is placed before a larger numeral, the smaller numeral is subtracted from the larger numeral. For example, IV is 4; the I is subtracted from V (5-1).
4. Only I, X, and C may be subtracted from a larger numeral. The “five” numerals (V, L, D) may not be subtracted from a larger numeral. 45 is written XLV, not VL.
5. When a smaller numeral is subtracted from a larger numeral, the smaller numeral can be no less than one tenth of the larger numeral. IX is 9, but IL is not permitted for 49, nor IC for 99. 49 is written XLIX and 99 is written XCIX. Only one numeral at a time may be subtracted and only from one other numeral. IIX is not permitted for 8, nor IXX for 19.
6. Always use the largest numerals possible. 15 is written XV, not VVV, even though writing three V's does not break rule #2. 