Total no. of questions =50 To choose one or more questions, 50C1+50C2+50C3......+50C50 .......(1) 50C0+50C1+50C2.....+50C50=250 50C1+50C2+50C3......+50C50=250−50C0 50C1+50C2+50C3+.....+50C50=250−1 Put in equation (1) 50C1+50C2+50C3+.......+50C50=250−1