This edition has been thoroughly revised and enlarged by including questions which appeared in the competitive examinations for Civil Services and Engineering Services conducted by UPSC and also from GATE conducted by IIT. The book was highly appreciated by the readers from all nooks and corners of the country. A large number of questions from the book appeared in the competitive examinations. The main features of the book were its conciseness coverage of entire syllabus in fewer questions and the Appendix B giving explanation to the correctness of a particular answer for some typical questions. Even after fifteen years the book is still considered to be a must for all those appearing in all sorts of competitive examinations.