Mahendras is a very good institute for only those students who have been studied the whole syllabus before hand and just come for a revision purpose. If you are a fresh candidate then you will not get much from Mahendras as it does not provide a detailed and thorough discussion on topic. They will just give a brief overview of the topic and make you practice 5 to 6 questions and nothing else. All the understaings is to be done by you only. They will not clear your small doubts they just say to come to their discussion session but its a waste they will just solve some question which is given by majority of students and not by the individual.
So I would say that its really a great place to prepare for banking, ssc and railway but for only those who have already srudied the syllabus beforehand.
