How many 4 -digit numbers can be formed by using' the digits 1 to 9 'if repetitions of digits is not allowed?

Explanation

Here order matters for example 1234 and 1324 are two diferent numbersiefherefore, there will be as many 4 digit numbers as there are permutations of 9 different digits taken 4 at a timẹ.
Therefore, the.required 4 digit `=9 ^prime P_4=9 !/(9-4) !=9 !/5 !=9 xx 8 xx 7 xx 6=3024`