Brain-Teasers Puzzles Riddles (vol 1)

1.
Three ants are sitting at the three corners of an equilateral triangle.
Each ant starts randomly picks a direction and starts to move along the edge of the triangle.
What is the probability that none of the ants collide?

2.
Four people need to cross a rickety bridge at night.
They have only 1 torch and the bridge is too dangerous to cross without one.
The bridge is only strong enough to support two people at a time.
Not all people take the same time to cross the bridge.
If these people cross the bridge individually, they will take: 1Min, 2Mins, 7Mins, 10Mins.
What is the shortest time needed for all four of them to cross the bridge?

3.
You are standing before two doors.
One of the path leads to heaven and the other one leads to hell.
There are two guardians, one by each door.
One of them always tells the truth and the other always lies, but you don’t know who is the honest one and who is the liar.
You can only ask one question to one of them.
What is the question, that will help you know the door to the heaven?

4.
There is a building of 100 floors.
If an egg drops from the Nth floor or above it will break.
If it’s dropped from any floor below, it will not break.
You’re given 2 eggs.
Find N, while minimizing the number of drops for the worst case.

5.
Every man in a village of 100 married couples has cheated on his wife.
Every wife in the village instantly knows when a man other than her husband has cheated, but does not know when her own husband has.
The village has a law that does not allow for adultery.
Any wife who can prove that her husband is unfaithful must kill him that very day-end.
The women of the village would never disobey this law.
They also know when someone killed her husband.
One day, a saint visits the village.
Before leaving, he announces that at least one husband has been unfaithful.
What happens now?

6.
You are blindfolded.
10 coins are placed in front of you on a table.
5 coins are head up and 5 coins are tails up.
You are allowed to touch the coins, but can’t tell which way up they are by feel.
How do you make 2 piles of coins each with the same number of heads up?
You can flip the coins any number of times.

7.
A man has 2 sticks of varying thickness.
These sticks are not identical.
They have different density & different length & different width.
Each stick burns in 60 minutes.
You have to measure 45 mins.
None of the sticks can't be cut into half.

8.
Estimate the circumference of earth.

9.
Estimate the number of human babies born on earth every year.

10.
You are put in an empty cubic room (no windows/doors).
All 4 walls, the roof, & the floor, are covered with mirrors.
How many total reflections will you see of yourselves?

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