Good = Possessing desirable qualities; adapted to answer the end designed; promoting success, welfare, or happiness; serviceable; useful; fit; excellent; admirable; commendable; not bad.
Synonyms: satisfactory, acceptable, solid, superb, high-quality, fine, excellent, superior.
Example – He is very good at his work.
Usage in Sentence: Good at, not in.
Don’t say: My sister is good in mathematics.
ü Say: My sister is good at mathematics.