Question

The number of different four digit numbers that can be formed with the digits 2, 3, 4, 7 and using each digit exactly once, is
(a) 120
(b) 96
(c) 24
(d) 100

Answer 1

Since each digit is used exactly once, for four digit number, _ _ _ _
First place has 4 options:
Second place has 3 options left
Third place has 2 options left
and Last place has 1 option
Therefore, number of different four digit numbers positive
= 4 × 3 × 2 × 1
= 24