Join the dots (number) 1, 4, 7 from top to bottom. then 7, 5, 3, diagonally up, then come to 2, 6, 9, 8.

1          2           3              1        2       3

4           5          6             4       5       6

7          8          9              7       8        9

Answer to Game No 18: We Are Even

Because the girl took only 50 cents from her friend, that is why she owed her friend 50 cents, BUT
The girl did not give her friend any 50 cents from her own money that is why her friend did not owe her any money.
When the girl said - "You give me only 50 cents." that made clear that she owed the money to her friend. To owe to the girl, the girl should first return her friend's money to her.

Answer to Game No 19: Toothpick Triangles

Make a square with four toothpicks, and put two toothpicks crossing each other diagonally in the square.

Answer to Game No 20: Some More Toothpick Problems

1. Writing 10 with nine sticks. You will see that writing TEN in words takes only 9 sticks.
2. Writing 0 with 4 sticks - write it like it is written in digital watches with 2 sticks on each side and 1 stick on top and 1 stick on bottom