Permutations and Combinations

Number of combinations of choosing 4 digits out of 4
=‌5C4=5
Each 4-digit set can be arranged in 4! ways =24 ways
So, total number of 4 -digit numbers
=5×24=120
In each group, each digit appears
‌

24

4

=6‌ times ‌
So, contribution per group
=‌ sum of digits ‌×6×(1000+100+10+1)
Now, compute total sum of digits for all 5 groups
&(2+3+5+8)+(1+3+5+8)
+(1+2+5+8)+(1+2+3+8)
+(1+2+3+5)
‌‌=18+17+16+14+11=76
‌‌=76×6666
‌‌ Hence, total sum ‌=506616