Logic riddles

12 men walking by,
12 pears hanging high,
Each took a pear,
There were left eleven there,
How?

Answer

Each was the name of one of those 12 men walking by and Each was the only one who took a pear.

I am green but not a tree. You can see me and sit on me and I grow around the world.
What am I?

Answer

Grass.

George is a butcher. Her feet are size 8, and she is 5 foot 11.
What does she weigh?

Answer

Meat. He is a butcher.

12 + 13 = 5
14 + 13 = 7
11 + 15 = 6
17 + 18 = ?

Answer

15

You are sitting with one opponent at an empty, round table. Taking turns, you should place one euro on the table, in such a way that it touches none of the coins that are already on the table. The first player that is not able to place a euro on the table has lost. By tossing a coin, it has been decided that you may start.
Which strategy will you follow to make sure you are guaranteed to win?

Answer

Put the first euro exactly in the middle of the table. Place each next coin "mirrored" to the coin your opponent has just placed: draw an imaginary line from the last coin of your opponent, through the center of the table, and place your coin on that line, exactly as far from the center of the table as your opponent's coin. In this way, you are sure that you can always place a euro and that your opponent is the first one that can no longer place a euro.

A women lives alone on the 30th floor and hates taking the stairs. Every day she takes the elevator down to the lobby floor to go to work. When she comes homes from work, she takes the elevator to the 20th floor and walks the rest of the way up, except on days when it rains. Those days she takes the elevator all the way home.
Why does she walk the last ten flights of stairs if she hates it so much?

Answer

The woman is too petite to reach the button for the 30th floor. She can only reach the 20th floor button. On days when it rains, she uses the umbrella to hit the button for the 30th floor.

9688 = 17
3105 = 6
3792 = ?

Answer

12

9+6 = 15; 8+8 = 16, then 17
3+1 = 4; 0 + 5 = 5, then 6
3+7 = 10; 9 +2 = 11, then 12

Flora killed several thousands of people without mercy. Afterwords, Flora disappeared and was never seen again. Yet the police never pursued her.
Why?

Answer

Flora was a hurricane.

There is a horse tied to a 6 meter rope. 7 meters away there is a pile of hay. The horse can easily eat the hay without moving its neck.
How does it do this?

Answer

The other side of the rope isn't tied to anything.

You are in a one-story house, and everything is blue. The floors, the ceiling, the walls, the tables, the chairs, everything is blue!
What color are the stairs?

Answer

It's a one story house! There are no stairs!