PHARMACEUTICAL MATH I PHRA 1209

• letters are designated as numbers

   i = 1

  v = 5

   

• repeating a unit twice doubles its value

   ii =2

  xx =20

   

• repeating a unit 3 times triples its value

  iii = 3

  xxx = 30

   

• roman numerals may only be repeated 3 times

• when a small roman numeral follows a larger roman numeral, add the two

XV = (10 + 5 ) =15

LX = (50 +10) = 60

 

• when a smaller value roman numeral comes before a larger roman numeral, subtract the first one from the second

XL = (50 - 10) = 40

CM = (1000 - 100) = 900

IX = (10 - 1) = 9

 

• when a smaller value roman numeral come, between two larger ones, subtract the smaller value roman numeral from the larger value that follows it, then add that to the remaining roman numeral

XIX = 10 + (10-1) =  (10 + 9) = 19

XXIX = 20 + (10-1) = (20 + 9) = 29

 

• use the least number of letters

VL = 45  (correct) versus  XLV = 45  (incorrect)