By adding the suffix –mente, you can form almost all adverbs for the adjective of feminine singular form. For e.g. Lets take “esatta” which means “exact”. Adding –mente to “esatta”; would become “essattamente” and would translate to “exactly”. But, there are some adverbial forms that differ, from the above –mente adverbial suffix. For e.g. “Cattivo” meaning Bad and “Buono” meaning good, have two different adverbial forms of “bene” meaning well and “male” meaning badly.
Moreover, in some places some singular adjectives, especially singular masculine adjectives are used in various averbial forms. For E.g. try the following sentances below.
‘Sempre risponde giusto’, which translates to A feminie form, meaning “She always answers correctly.”
Or
‘Parlo Piana’, which translates to “He is speaking softly”.
Or
‘Abitano Vicino’ which means “They live nearby”
Hence, blindly adding “-mente” would not be sufficient always, and adverbs or adverbial sentences, sometimes require some manipulation