XLV

according to my 12 year old XLV

It would be XLV

IDK, I thought is was VL, but everyone else says different. V-5 X-10 L-50

This is conventionally written: XLV But the Romans themselves would originally have written: XXXXV or *any* combination which sums to 45, such as XIVIVVIVIX if it is convenient. The idea of "XL" meaning 40 would originally have been regarded as stupid and incorrect to a Roman. Start with XL and take away the X and you'd end with more than you started with! However, the combination XXXX was particularly irksome to write or carve, so the abbreviation XL was for forty was invented and this can be seen above the doors in the Colloseum. This is the first and only subtractive number used at that time. XL was still seen as an abbreviation. You would still have to convert that into four stones in the X column of the abacus before you could do arithmetic. Contrary to popular belief, arithemtic in the pure additive roman number system is easier than in decimal. For example: Roman multiplication table: X times X = C X times C = C times X = M X times V = V times X = L X times L = L times X = D V times V = XXV L times L = MMD V times L = L times V = CCL eleven sums to memorize compared to eighty-one in the corresponding modern decimal multiplication tables. Note: D and M for 500 and 1000 are also inventions. Originally these were I) and CI) where the ) should be symmetric with the C.

xxxxv

XLV. I believe.

This question has already been answered several times. The correct answer is XLV.

XLV "Roman numerals are not a purely additive number system. In particular, instead of using four symbols to represent a 4, 40, 9, 90, etc. (i.e., IIII, XXXX, VIIII, LXXXX, etc.), such numbers are instead denoted by preceding the symbol for 5, 50, 10, 100, etc., with a symbol indicating subtraction. For example, 4 is denoted IV, 9 as IX, 40 as XL, etc. However, this rule is generally not followed on the faces of clocks, where IIII is usually encountered instead of IV. Furthermore, the practice of placing smaller digits before large ones to indicate subtraction of value was hardly ever used by Romans and came into popularity in Europe after the invention of the printing press (Wells 1986, p. 60; Cajori 1993, p. 31)." Source: http://mathworld.wolfram.com/RomanNumerals.html Please notice that "V", "L", and "D" can never be subtracted, so "VL" is not acceptable for 45.