Question

How many different numbers of six digits each (without repetition of digits) can be formed from the digits 4, 5, 6, 7, 8, 9?
How many of these are not divisible by 5?

Answer 1

Here we have to use all six digits 4, 5, 6, 7, 6, 9.
$\therefore$ Number of six digit numbers = 6! = 720.
Now 5! numbers are divisible by 5 as 5 is fixed in the last place.
Hence total no. of numbers which are not divisible by 5 is
$6!-5!=720-420=600$.