The number of four digit numbers that can be formed with the digits 1,2,3,4 and 5 in which atleast two digits are identical is
The correct option is D. 54−5!
The number of four digit numbers formed by the digits 1,2,3,4 and 5 , when repetition is allowed = 54
The number of numbers when repetition not allowed =5!
∴ The required number of numbers =54–5!