What is the number of four-digit decimal numbers `(lt 1)` in which no digit is repeated ?

The number of natural numbers less than 1000, in which no two digits are repeated is

Find number of four-digit numbers in which repetition is not allowed. Also find number of four-digit numbers in which at least one digit is repeated.

Find number of four-digit numbers in which repetition is not allowed. Also find number of four-digit numbers in which at least one digit is repeated.

Find number of four-digit numbers in which repetition is not allowed. Also find number of four-digit numbers in which at least one digit is repeated.

The number of four digits telephone numbers having atleast one of their digit is repeated

The number of five digit telephone numbers none of their digits being repeated is

The number of four digit telephone numbers having at least one of their digits repeated is: (Note: 0 can be accepted in first place)