Question

The average of four digit numbers that can be formed using each of the digit 3,5,7 and 9 exactly once in each number is?

Answer 1

Generally the sum of all the numbers which can be formed by using the n distinct digits, is given by the formula:

(n-1)!*(sum of the digits)*(111…..n times)

Here the given digits are 3,5,7 and 9.

So, n= 4

Sum of all the numbers formed by these digits

= (4-1)! (3+5+7+9) (1111)

=159984 (3!=6)

Number of numbers formed by 4 digits = 4! = 24

So, average = 159984/24=6666