KCC's Quizzes: Strange Coding

2

Each digit in the 4 digit number has a value associated with it, and the result is the sum of those values.

1111, 2222, 3333, 5555, and 7777 all have zero as a result, so 1, 2, 3, 5, and 7 digits are all have a value of zero.

0000, 6666, and 9999 have 4 as a result, so 0, 7 and 9 have a value of 1.

8809 =6, so the digit 8 must have a value of 2 (2+2+1+1)

From the above we now know that 2581=0+0+2+0=2

Counting the number of loops in each digit as Mark answered with also explains why the digit 4 doesn't show up at all.  I guess it's not clear if 4's have a loop/enclosed space or not! 

Counting the number of loops in each digit as Mark answered with also explains why the digit 4 doesn't show up at all.  I guess it's not clear if 4's have a loop/enclosed space or not! 

No, 4 cannot be considered... If so, 2 can be in similar case.