Incorrect spelling


Incorrect spelling, explanation: this form is wrong, as there should be no i in mandatory. The word is created from mandate (a noun and a verb), which is also spelled with a instead of i. Therefore manditory is incorrect and the correct spelling is mandatory.

Correct spelling


Correct spelling, explanation: this spelling is the correct one, because the adjective mandatory is made from the noun and verb mandate, which is also spelled with a. Latin origin mandatum also points to mandatory as the correct form, so maditory is a mistake.

Definition of mandatory:
adjective, compulsory, ordered by an authority
You don’t have to do this project for school, it’s mandatory only for senior students.
Wearing seatbelts is mandatory at all times.