Question

How maany 4 digit numbers formed with the digits 1,2,3,4,5

Answer 1

If we can repeat the digits , Then for each number we have 5 choices

so it would be 5x5x5x5 => 625
( we multiply 5 , 4 times because we require a 4 digit number )


However if we are allowed only to use each digit once , then

we would have 5 choices for 1st digit , 4 for 2nd digit , 3 for 3rd digit and 2 for 4th digit


So the answer would be 5x4x3x2 => 120 //