Unfaithful wives

Solve this logical puzzle-
An anthropologist studying a primitive tribe in a remote location in the Amazon basin, had uncovered a strange tribal custom. Whereby, if a husband found out his wife was unfaithful to him, he must execute her in a public ceremony in front of the whole tribe on the same day at midnight. It so happened that every man in the tribe knew about every cheating wife except his own, since telling a man about his cheating wife was against the tribal honor code. On the day of his departure, the anthropologist held a tribal meeting and made the announcement: “I know there are unfaithful wives in this tribe.” On the ninth day thereafter all cheating wives were executed at the same time.
How many unfaithful wives were there?

Philosopher's Clock

One absentminded ancient philosopher forgot to wind up his only clock in the house. He had no radio, TV, telephone, internet, or any other means for telling time. So he traveled on foot to his friend’s place few miles down the straight desert road. He stayed at his friend’s house for the night and when he came back home, he knew how to set his clock.
How did he know?

DEATH

You've been sentenced to death in an obscure foreign country which has a strange law. Before the sentence is carried out, two papers -- one with "LIFE" written on it and one with "DEATH" written on it -- are folded up and placed in a hat. You are permitted to pick out one of the papers (without looking), and if you choose the one with "LIFE" written on it, you are set free. Otherwise, the death sentence is carried out. On this occasion, an enemy of yours, bent on your demise, has substituted the paper with "LIFE" written on it with another one with "DEATH" written on it. Now both the papers from which you have to pick out are written “DEATH” on them. This person informs you of what he has done and that you are doomed to die. You are not permitted to speak to anyone about this misdeed, nor will you have a chance to switch the papers or the hat yourself in time. How will you avoid certain death?

Lady And Tiger II

If a lady is in Room I, then the sign on the door is true, but if a tiger is in it, the sign is false. In Room II, the situation is the opposite: a lady in the room means the sign on the door is false, and a tiger in the room means the sign is true. Again, it is possible that both rooms contain ladies or both rooms contain tigers, or that one room contains a lady and the other a tiger. The signs on the doors of the rooms are as follows:

Room1:BOTH ROOMS CONTAIN LADIES
Room2:BOTH ROOMS CONTAIN LADIES

Which door should you open (assuming, of course, that you prefer the lady to the tiger)?

Solution:
Since the signs say the same thing, they are both true or both false. Suppose they are true; then both rooms contain ladies. This would mean in particular that Room II contains a lady. But we have been told that if Room II contains a lady, the sign is false. This is a contradiction, so the signs are not true; they are both false. Therefore, Room I contains a tiger and Room II contains a lady, so you should choose Room II.

Lady And Tiger

This is the first puzzle of a series of classic "Lady or the Tiger" puzzles. You have to choose between two rooms. Each of them contains either a lady or a tiger, but it could be that there are ladies in both rooms, or tigers in both rooms, or one could contain a lady while the other contained a tiger. There are signs on the doors of the rooms:

Room 1:IN THIS ROOM THERE IS A LADY, AND IN THE OTHER ROOM THERE IS A TIGER .

Room 2:IN ONE OF THESE ROOMS THERE IS A LADY, AND IN ONE OF THESE ROOMS THERE IS A TIGER .

One of the signs is true, but the other one is false. Which door would you open (assuming, of course, that you preferred the lady to the tiger)?

Masters of Logic Puzzles (dots)

Three Masters of Logic wanted to find out who was the wisest amongst them. So they turned to their Grand Master, asking to resolve their dispute. “Easy,” the old sage said. "I will blindfold you and paint either red, or blue dot on each man’s forehead. When I take your blindfolds off, if you see at least one red dot, raise your hand. The one, who guesses the color of the dot on his forehead first, wins." And so it was said, and so it was done. The Grand Master blindfolded the three contestants and painted red dots on every one. When he took their blindfolds off, all three men raised their hands as the rules required, and sat in silence pondering. Finally, one of them said: "I have a red dot on my forehead."
How did he guess?

Microsoft Puzzle : Coins on the Table

There is a table on which a number of coins are placed. You also know that there are as many coins with Head up as many coins with Tail up. Now you have to divide the coins (number of coins is even) into two equal piles such that number of coins with Heads up and Tails up in either piles be the same. The catch is you are blind folded and you cannot determine the sides (for sure) if you are blinded