railway RRB NTPC Mock Test Series 2024-25 (CBT 1 + CBT 2) Quantitative Aptitude Permutation and Combination
A competitive exam has 20 questions with four options each. The number of ways in which a student can attempt all questions if he has a option to leave the question also is ?
1
420
2
520
3
420 - 1
4
520 -1