"Learnt" and "learned" are two acceptable forms of the past simple/past participle of the verb learn, which means exactly the same thing. Learnt is an irregular verb in the British English where the past tense is spelt with a `t` at the end - [learn/ learnt]. Conversely, Learned is a regular verb in the American English where the past tense is spelt with a `ed` at the end - [learn / learned]. Thus,neither is incorrect as `learnt` is more commonly used in the British English, and `learned` in American English. Using anyone of these two forms are correct and are up to your preference. However, you would want to use the one that is more widely used or accepted in your country. When using any one of these forms you must use it consistently in your writings and don`t interchange your use of them. In other words, avoid mixing the `ed` and the `t` endings in your writings. There`re other forms of verbs of the past simple/past participle in both American and British English.
Some of these are:
- smelt/smelled etc