How many four digit numbers are there with distinct digits?

Explanation

The number of all four digits number with a distinct digit is made from
`0 to 9`

These ten digit have to be put in it places. Thousands, hundreds, tens units

Obviously, `0` cannot take the thousands place because it will become three digit number, so for thousands `9` ways can bedone

Now . and other `8` digit left, so at hundrend place `9` ways to set a digit.

We are now left with `8` digit fill the tens place which can be done in `5` ways

The remaining `7` digit in the unit place in `7` ways
so the answer is
`9xx9xx8xx7=4536 `