A brain teaser kind of question at GregTang math (I just heard bout GregTang and the problem recently at a school event): use 6, 7, 8 and 9, plus any addition, subtraction, multiplication and division to make the result of calculation as 10 (only use each number once, can use any kind of parenthesis as needed).
I saw a few kids come up with answers (but it seems to me some answers are from the parents 🙂 I tried but could not come up with answer as 10 at the spot. Note we, my wife and I, when we were kids in China did similar exercise / games using the poker (draw 4 kids, instead of 10, we need to make 24). On my way home, or at home (this is how things work for me, just like how I come up with the solutions to coding at work), I have this: (7+8)x6/9=10
Note: there should be many ways / combinations to this, the one I heard at the gathering is 8x(9-7)-6=10
After that I followed GregTang on twitter, and I worked on some of the puzzles there from time to time: those are not “too hard” problems, but nonetheless interesting / educational for the kids (I think).