I will give riddles and whenever one is answered I will give a new one, there will be no prize, it is just for fun

Here is the first riddle;

Two spies want to get in an enemy's military base. In order to get in they have to give the correct countersign to the guard at the gate after he gives them the sign. So they wait hidden nearby the gate so that they will overhear the countersign from another soldier.

One soldier comes and the guard gives the sign six. The soldier answers three. The guard lets him pass. Another soldier comes. The guard says twelve and the soldier gives the answer six. The guard lets him pass. So, the first spy goes to the gate and the guard says ten. The spy, sure that he knew the answer, says five. Immediately, the guard shoots him dead.

The other spy, who saw that the other spy was killed, walked up to the gate. The guard gave the number seven, the spy got the answer correct. What was his answer?
Explain how you got your answer.

I'm going for five, with the answer being the amount of letters in the sign.

Yeah, I also think that this is the answer.

8898=7
4566=2
1203=1
2313=0
4566=2
5464=1
7774=0
9856-4
9952=2
1886=5
1231=0
8764=3

4500=?

(hint: they say it's much easier for young children than for adults)

2 ?

My answer is 2 (a child would look at the numbers for shapes, only shape that matches up with numbers is circles)
If correct someone else can go

It could be two as well.

{6, 3} -> 6 + 3 = 9
{12, 6} -> 1 + 2 + 6 = 9

{10, 5} -> 1 + 0 + 5 = 6 (NOT nine)

{7, 2} -> 7 + 2 = 9

The problem with the first spy's logic is that it was too obvious. That's the problem with your answers as well! :D

That was quick! Here is another one

A man went to visit an acquaintance at a mental asylum. After the visit he decided to go to the Director's office and questioned him on the criteria that defines if a patient should be institutionalized.

"Well," said the Director, "We give them a simple test: First we fill up a bathtub. Then we offer a teaspoon, a teacup, and a bucket to the patient and ask the patient to empty the bathtub."

"OK, that's really easy. Of course I would choose the bucket! It is much larger than the spoon." answered the man

Why was this man taken to the admissions office instead of being allowed to leave?

Because anyone who's not a dumbass would just remove the plug from the tub :P

Agreed. This was way too easy. But what about the solutions to the previous one?

The first thought that came to my mind was "Break it or turn it on its side!"... I guess I belong to a mental asylum D:

Pretty sure my answer is correct

Wasn't this the puzzle from Monkey Island 2? :D

Yes, all the answers are correct! (and in a way, even " "Break it or turn it on its side!"... I guess I belong to a mental asylum D:" is also correct when taken in its entirety ;)

I'll end my "thread hijacking" (sorry NoMoreGoodNames!, I hope you didn't mind) with a classic one, the Monty Hall Question

Monty Hall was the presenter for the "Let's make a Deal" TV Contest. One night at the end of the program he gave the winner a choice of four doors: Behind one door is a car; behind the others, goats. The contestant chose door number 4 and Monty said "I don't know which door has the car, but our producer does, so let me show you and our viewers something interesting!" after a drum roll, an assistant came on stage and opened door number 1 to show a goat. Then Monty took a coin and said "heads for door number 2 and tails for door number 3". The coin landed on tails and Monty told the contestant "Maybe your first guess was wrong so I'll give you a chance to switch to door number 3. What would you like to do?"

The questions - What would you choose if you were the contestant? Why?

Notes:
* Monty Hall is an actual TV Personality but the story has been fictionalized and spiced up a little from the classic version, to make it more interesting
* You'll find plenty of analyses if you do a web search for "Monty Hall Question"
Credits:
* The 3 questions that I posted were taken from homework 4 of the MOOC https://www.coursera.org/course/businessandphilo