Learn English – Is it appropriate to use “it’s the bread and butter” in formal english

formalityvocabulary

I am preparing for an English language test. That is why I am working on strengthening my English vocabulary.

My question is regarding the speaking section of the test.

If the examiner asks me about a particular subject, for example mobile development, would it be too informal to say "it's my bread and butter"?

If yes, then could you please suggest to me a word for that? I don't want to write a sentence like "that is how I make money or that is the source of my income"

Thank you.

PS: If you find any grammatical or spelling mistakes in this question then please do let me know. I would appreciate that.

Best Answer

Your English was generally good, but I have made some amendments in my editing which you might care to review. They mostly concern punctuation, but remember the definite article and prepositions are important too.

No, I see nothing wrong with using the 'bread and butter' metaphor. If I were the examiner I would be impressed that you were showing a grasp of everyday colloquial English.