Question

The number of natural numbers from 1000 to 9999 (both inclusive) that do not have all 4 different digits are?

Answer 1

Total number of numbers from $1000$ to $9999$ is $9999-1000+1=9000$

Numbers that have all four different digits $=9\times 9\times 8\times 7=4536$

Hence the number of numbers that do not have, all $4$ different digits $=9000-4536$

$=4464$.