Find the number of `n` digit numbers, which contain the digits 2 and 7, but not the digits 0, 1, 8, 9.

The number of n-digit numbers which contain the digits 2 and 7, but not the digits 0,1,8,9, is

The number of 3- digit numbers containing the digit 7 exactly once :

Let N be the number of 4- digit numbers which contain not more than 2 different digits. The sum of the digits of N is :

If the number of 6 digit numbers which contain exactly 4 different digits such that exactly one digit repeats is k(7!) then find k

The total number of 9-digit number which have all different digits is

Total number of 6-digit numbers in which only and all the five digit 1,2,5,7 and 9 appear, is :

Total number of 6 -digit numbers in which only and all the five digits 1,3,5,7 and 9 appear,is