find the mean of all possible 4-digit numbers created using the digits2,5,7,9?

Question

to find mean just add all the given numbers and divide how many numbers are there,ex.1+2+3+4+5=15 divide to 5=3

Answer 1

If repeat is allowed we have 256 numbers.
but I assume repeat is not allowed.
so we have 4*3*2*1=24 numbers
6 numbers of these 24 numbers have 2 in the first digit of right(one digit)
6 numbers of these 24 numbers have 5 in the first digit of right(one digit)
6 numbers of these 24 numbers have 7 in the first digit of right(one digit)
6 numbers of these 24 numbers have 9 in the first digit of right(one digit)
know we can add first digit of right for these 24 numbers
6*(2+5+7+9)=138
6 numbers of these 24 numbers have 2 in the 2nd digit of right(ten digit)
6 numbers of these 24 numbers have 5 in the 2nd digit of right(ten digit)
6 numbers of these 24 numbers have 7 in the 2nd digit of right(ten digit)
6 numbers of these 24 numbers have 9 in the 2nd digit of right(ten digit)
know we can add 2nd digit of right for these 24 numbers
6*(2+5+7+9)=138
and cuz it ten digit we have
138*10=1380
6 numbers of these 24 numbers have 2 in the 3rd digit of right(hundred digit)
6 numbers of these 24 numbers have 5 in the 3rd digit of right(hundred digit)
6 numbers of these 24 numbers have 7 in the 3rd digit of right(hundred digit)
6 numbers of these 24 numbers have 9 in the 3rd digit of right(hundred digit)
know we can add 3rd digit of right for these 24 numbers
6*(2+5+7+9)=138
and cuz it hundred digit we have
138*100=13800
6 numbers of these 24 numbers have 2 in the 4th digit of right(thousand digit)
6 numbers of these 24 numbers have 5 in the 4th digit of right(thousand digit)
6 numbers of these 24 numbers have 7 in the 4th digit of right(thousand digit)
6 numbers of these 24 numbers have 9 in the 4th digit of right(thousand digit)
know we can add 4th digit of right for these 24 numbers
6*(2+5+7+9)=138
and cuz it thousand digit we have
138*1000=138000
now if we add all
we have
138000
+13800
+1380
138
=153318
mean=153318/24=6388.25
try to solve it if repeat is allowed.
if you can't I'll help.
Sorry for my English.

Answer 2

The answer is 6388.25 and is derived by adding all of the number combinations together of which, given the numbers 2, 5, 7 & 9 there are 24 possible combinations, the sum of which is 153,318. Divide that figure by the total number of possible combinations ( in this case 24) and you get the answer of 6,388.25

Answer 3

Start out with the biggest possible number, then work your way down to the smallest.

The biggest set of numbers:

9752
9725
9572
9527
9275
9257

Smallest:

2579
2597
2795
2759
2957
2975

Find the ones beginning with 5 and 7, then add and divide by 24 (which will be the total of all possible numbers.)