I would like to ask you if you can help me to know why we put ly to careful when we transform it from Adj. to Adv. while we delete e from gentle and we add y to be gently why do not we put just y to careful o be carefuly???????
Ah, the impossible vagaries of English spelling.
One reason may be because, with careful pronunciation, you will notice that carefully adds a syllable to careful, whereas gentle and gently are both 2-syllable words.