## Thinking Mathematically (6th Edition)

$CXXIX$
RECALL: $C=100 \\L=50 \\X=10 \\V=5 \\I=1$ When a smaller number is written before a bigger number, the smaller number is subtracted to the bigger number. Note that: $129 = 100 + 20 + 9 \\129 = 100 + 10 + 10 + (10-1) \\129=CXXIX$