Question

Write the numbers 1 to 9 in the circles so that each side of the square adds up to 12. (Hint:put 7 in the middle)
Example: this is the grid u have to put the numbers in
O------O-------O
| |. |
O------O-------O
|. |. |
O------O-------O

Answer 1

9 clearly cannot be on a corner, so we have

X9X
X7X
XXX

Now, the only choices along the top are 1,2, so we have

192
X7X
XXX

8 cannot be on a corner, because then we'd need 2,2 or 1,3 twice. It must be on one of the sides:

192
87X
3XX

Now, 3+9=12 and 2+10=12
We still need to place 4,5,6

3,6,3 is out, so 4+8=12 makes for

192
876
354