Dennis Coble, @DennisCoble, just tweeted me this challenge an hour ago.
Here’s 1 that might interest you. Numbers 1-9 all used: 3 digit number, plus or minus 3 digit number, gives another 3 digit number.
As usual, the problem is deceptively simple, as is the solution. However, students could be engaged in their activity of this task for a full period. 😉 And the ordering of student ability and success could be shaken. 🙂