ROMAN NUMERALS
One of the earliest systems of writing numerals is the Roman Numeral system. This system is still in use in many places. For example, some faces of clocks show hours in Roman numerals; we use Roman numerals to write numbered list; etc.
Unlike the Hindu-Arabic numeral system, Roman numeral system uses seven basic symbols to represent different numbers. The symbols are as follows :

The Roman numerals :
I, II, III, IV, V, VI, VII, VIII, IX, X  denote 1,2,3,4,5,6,7,8,9 and 10 respectively. This is followed by XI for 11, XII  for 12,... till XX for 20. Some more Roman numerals are :
I     V     X      L      C      D        M
1    5     10    50   100   500    1000
The rules for the system are :
(a)    If a symbol is repeated, its value is added as many times as it occurs: i.e. II is equal 2, XX is 20 and XXX is 30.

(b)    A symbol is not repeated more than three times. But the symbols V, L and D are never repeated.

(c)    If a symbol of smaller value is written to the right of a symbol of greater value, its value gets added to the value of greater symbol.
VI = 5 + 1 = 6, XII = 10 + 2 = 12 and LXV = 50 + 10 + 5 = 65

(d)    If a symbol of smaller value is written to the left of a symbol of greater value, its value is subtracted from the value of the greater symbol.
IV = 5 – 1 = 4, IX = 10 – 1 = 9
XL = 50 – 10 = 40, XC = 100 – 10 = 90

(e)  The symbols V, L and D are never written to the left of a symbol of greater value, i.e. V, L and D are never subtracted.
The symbol I can be subtracted from V and X only.
The symbol X can be subtracted from L, M and C only.
Following these rules we get,
1 = I              10 = X             100 = C
2 = II             20 = XX
3 = III            30 = XXX
4 = IV           40 = XL
5 = V            50 = L
6 = VI           60 = LX
7 = VII          70 = LXX
8 = VIII         80 = LXXX
9 = IX           90 = XC

Ex :    Write in Roman Numerals
(i) 69        (ii) 98.
Sol:  (i) 69 = 60 + 9  = (50 + 10) + 9 = LX + IX  = LX IX
(ii) 98 = 90 + 8     = (100 – 10) + 8 = XC + VIII = XCVIII