If,

29 - 1 = 30

9 - 1 = 10

14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?

11 - 1 = 10 ?

XI - I = X

Remove I (Roman equivalent of number 1) from the LHS, you will the get the number on the RHS.

29 - 1 = 30

XXIX - I = XXX

14 - 1 = 15

XIV - I = XV

9 - 1 =10

IX - I = X

Similarly,

11 - 1 = 10

XI - I = X