Four digit numbers are formed using each of the digits 1, 2, ..., 8 only once. One number from them is picked up at random. The probability that the selected number contains unity is
Answer & explanation
Correct answer: option 3
Total number of four digit numbers formed with the digits 1, 2, 3, ....8 is $ {^8C}_4 × 4!$
Number of four digit numbers formed with the digits 1, 2,..... , 8 and containing unity as one of the digits is
$ {^7C}_3 × 4!$
Hence, required probability = $\frac{^7C_3 × 4!}{^8C_4 × 4!}=\frac{1}{2}$