"-tant" or "-tent"?

On the first mid-term, many students misspelled the word "persistent." Instead of "ent," they ended the word with "ant."

The following is a chart listing adjectives ending with "tant" and "tent." Can you figure out the rules?

 

-tant	-tent
important constant instant  resistant  militant  exorbitant  (in)tolerant repentant hesitant	impotent insistent consistent  persistent  existent  competent  remittent