The numerals from 40 through to 60 are as follows, with their value in brackets after each numeral... XL (40) XLI (41) XLII (42) XLIII (43) XLIV (44) XLV (45) XLVI (46) XLVII (47) XLVIII (48) XLIX (49) L (50) LI (51) LII (52) LIII (53) LIV (54) LV (55) LVI (56) LVII (57) LVIII (58) LIX (59) LX (60).
It is: 60 = LX
40 = XL
40 in roman numerals is XL (10 less than 50) and 60 is LX (10 more than 50).
40 = XL
60 - 100 is the same as LX - C in Roman numerals
It is: 60 = LX
LX
XL
The Roman numeral for 40 was XL.
XL meaning: -10+50 = 40
XL
XL