Math tips, Math formulas

Roman Numerals
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You can guess from their name that Roman Numerals originated in ancient Rome. They were created as a simple means of counting in which certain letters are given values as numerals (a numeral is a written symbol referring to a number). The original system of Roman Numerals was modified during the Middle Ages and is the system we still use today.
Seven letters form the basis of Roman Numerals. Each letter stands for a number as shown here.
ROMAN NUMERALS
I = 1 V = 5
X = 10 L = 50
C = 100 D = 500
M = 1,000
Reading and Writing Roman Numerals
Numbers are represented by combining the letters shown above. There are several rules to follow.
If one or more letters are placed after another letter of greater value, add that amount.
VI = 6 (5 + 1 = 6)
XXVII = 27 (10 + 10 + 5 + 1 + 1 = 27)
MDC = 1,600 (1,000 + 500 + 100 = 1,600)
A letter cannot be repeated more than three times.
30 = XXX (10 + 10 + 10 = 30)
40 = XL (50 - 10 = 40) You cannot write 40 as XXXX.
If a letter is placed before another letter of greater value, subtract that amount.
IX = 9 (10 - 1 = 9)
XL = 40 (50 - 10 = 40)
CML = 950 (900 + 50 = 950)
You can only subtract powers of 10 (I, X, C).
95 = XCV (100 - 10 + 5 = 95)
You cannot write 95 as VC because V is not a power of 10.
You cannot subtract more than one number from another number.
18 = XVIII (10 + 5 + 1 + 1 + 1 = 18)
You cannot write 18 as IIXX.
By the way, there is no zero in the system of Roman Numerals.