Burt Kaliski Jr. (@modulomathy)
3/31/12 1:21 PM
#math trivia for #March31: #91 is XCI in Roman numerals. What other numbers this year only use the Roman powers of 10 (I, X and C)?
A Roman numeral can have as many as three consecutive Is, Xs and Cs, so a number in the 0s, 100s, 200s or 300s, plus 0, 10, 20 or 30, plus 0, 1, 2 or 3, will work. In addition, IX and XC can be used, so the tens contribution can also be 90, and the ones can be 9.
The possibilities in the range 1-366 are therefore:
— 1,2,3,9
— 10,11,12,13,19
— 20,21,22,23,29
— 30,31,32,33,39
— 90,91,92,93,99
— 100, and all of the initial set plus 100
— 200, and all of the initial set plus 200
— 300, and all of the initial set up to 39 plus 300
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