plugg or resolve?

[imanemekouar]

I have trouble determining when do I have to plug number or resolve the problem in a theorist way .
Is there some kin of question where pluging is more efficient?What is this kind of question?
How can I recognize them?
Please help.

[StaceyKoprince]

A short answer here, but this question should go in the General Math Questions folder. If you'd like a more extensive answer / discussion, please post there.

Generally, if you completely know the theory, then that's the most efficient way - but you really have to know the theory very well. If you don't, then testing numbers is better.

You can recognize that a problem might qualify for testing numbers if it has:
1) variables in the answer choices
2) percentages or fractions in the answers, along with no "real" numbers in the problem
3) (for DS) variables, percentages or fractions in the question and statements
4) a question that asks what MUST be true or false (or, sometimes, what COULD be true)

You can find more information about this in the VIC chapter of the Equations book, the Smart Numbers portion (DS chapter) of the Number Properties book and the Smart Numbers portions (multiple chapters) of the Fractions Decimals Percents book.