Ducing Number System Application for the preparation of Quantitative Aptitude for various companies like TCS, AFour, Persistent, Tech Mahindra and so on. Number System is most sections for modern exams and it is asked in almost all types of exams ranging from Campus Placement to Entrance Exams, some common exams are CAT, XAT, MAT, GRE, GMAT, SAT, NTSE and various bank exams.