Prof. K. L. Sehgal is currently professor in NSB (formerly NIILM School of Business) teaching several papers. He had very long, nearly 50 years, experience of teaching in various institutes. After finishing his M.Sc. (Maths), he completed his M.Stat. (from Indian Statistical Institute) in 1964 and immediately after completion he joined faculty of Indian Statistical Institute, Delhi, where from he retired in 1997. He had been visiting faculty to various institutes for some time and again joined NSB as regular faculty member. This book is outcome of his long association with students to fill a gap of having simple book on basic of mathematics.