zac08
Senior Member
A simple way to understand. X is 10. Any number they add before subtracts and any after adds. So,
9 = 10-1 = IX
11 = 10+1 = XI
19 = 10+9 = XIX (dont ask me why it isnt 10+1+10-1 - you can only use the 1 once ;p)
21 = 20+1 = XXI
Morning Maddy
Maths problem??
10+1+10-1 = 20 not 19 :sticktong