Correct spelling, explanation: the word interested is a past-participle adjective of the verb interest. The past participle is formed by adding -ed or -d to the end of the root form of the verb. Although the pronunciation may suggest a different spelling – intrested – this word originates from the Latin interesse. This is why the correct form of interest is interested, not intrested.

Definition of interested:
adjective, a willingness to engage in something
I am not interested in further cooperation with your company.
-Do you want to go out with me? -No, I’m not interested.

Phrasal verbs with interested:
interested in – having the attention engaged in something,
She is very interested in English culture.

Incorrect spelling, explanation: the spelling is a mistake since the past-participle adjective must accord with its root, which is the verb interest. When we derive a word, we have to pay attention to the original form and add -ed to the base. Therefore, intrested is an incorrect spelling and the correct one is interested.

Incorrect spelling

Incorrect spelling

Incorrect spelling