For Tetsuo
No, I don't think your dictionary is incorrect but maybe your dictionary is using and showing both American English and British Engish.I would like you to correct me if I'm mistaken once again. But accoriding to Longman dictionary of Contemporary English, Cambridge Learner's dictionary and Oxford Student's Dictionary it is good AT something. In Oxford Practical English Usage published by Oxford it is given a clear explanation of using the right preposition with good. It says:
good at (not in)
Are you any good at tennis?
No, I don't think your dictionary is incorrect but maybe your dictionary is using and showing both American English and British Engish.I would like you to correct me if I'm mistaken once again. But accoriding to Longman dictionary of Contemporary English, Cambridge Learner's dictionary and Oxford Student's Dictionary it is good AT something. In Oxford Practical English Usage published by Oxford it is given a clear explanation of using the right preposition with good. It says:
good at (not in)
Are you any good at tennis?