This problem can be solved by pre-school children in 5-10 minutes, by programer – in 1 hour, by people with higher education …

This problem can be solved by pre-school children in 5-10 minutes, by programer – in 1 hour, by people with higher education … Well, check yourself.

The answer has to do with how many circles are in each number. So the number 8 has two circles in its shape so it counts as two. And 0 is one big circle, so it counts as 1.

So 2581 = 2