Примеры

думать и гадать - to puzzle over it;
думу думать - to brood, to meditate;
и думать не смей - don't dare ;
как ты думаешь? - what do you think?;
много думать о себе - to be conceited; to think highly of oneself, to have a high opinion of oneself, to have an exalted opinion of oneself; to think no small beer of oneself ;
надо думать - it seems, most likely ;
надо думать - I should say so ;
не долго думая - without hesitation, without thinking twice, without a moment's thought;
не думать не гадать - never think or dream;
не думаю (едва ли) - I scarcely / hardly think so;
не думаю (едва ли) - I doubt it;
я думаю! (конечно) - I should think so!, of course!;