Place the digits from 1 tot 9 in every row, column and 3x3-block. Black dots in the grid imply that applying one of the binary operations (addition, subtraction, multiplication or division) on the two neighboring digits result in the number 8. If there is no black dot between adjacent cells, 8 cannot be produced by the two digits going through any binary operations.
Solution code: Row 2, followed by column 5.
on 21. July 2016, 11:56 by ohm0123
It's hard. But funny. Thanks Richard.
on 11. February 2014, 14:54 by Ours brun
Really nicely made. So much better than the average software-generated puzzle. Thanks Richard!
on 7. February 2014, 19:57 by CHalb
One of those where I really liked the way I had to think.
on 4. February 2014, 16:37 by Saskia
on 4. February 2014, 09:32 by Statistica
Tolles Rätsel, aber nicht so einfach!