Good

[heidita]

In British English, we don't use 'in' here much at all

I thought at was the only correct one. Interesting.

Even though, here in an exam, in would be marked as a mistake, it's a typical multiple choice question.

[Nain]

I thought it was

Good in maths

Good at calculating

Good with numbers

[stuartnz]

Here in NZ, we'd say "at". We also say "maths", too. I remember reading on antoher web forum someone complaining about the subtitling of a Hindi movie that used "maths". The person complained "math is not a plural!" and was genuinely surprised to learn that India, like many other Commonwealth countries, retains the "s" when contracting "mathematics". Vive la différence, as we say in English.