Hard riddles

logicmathshort

What time is it?

A man gave one son 10 cents and another son was given 15 cents. What time is it?
1:45. The man gave away a total of 25 cents. He divided it between two people. Therefore, he gave a quarter to two.
94.11 %
43 votes

logicprobability

Red and blue marbles

Your friend shows you two jars, one with 100 red marbles in it, the other with 100 blue marbles in it. He proposes a game. He'll put the two jars behind his back and tell you to pick one of them at random. You'll then close your eyes, he'll hand you the jar you picked, and you'll pick a random marble from that jar. You win if the marble you pick is blue, and you lose otherwise. To give you the best shot at winning, your friend gives you the two jars before the game starts and says you can move the marbles around however you'd like, as long as all 200 marbles are in the 2 jars (that is, you can't throw any marbles away). How should you move the marbles around to give yourself the best chance of picking a blue marble?
Put one blue marble in one jar, and put the rest of the marbles in the other jar. This will give you just about a 75% chance of picking a blue marble.
94.11 %
43 votes

cleanlogicshort

Longer line

You draw a line. Without touching it, how do you make the line longer?
You draw a shorter line next to it, and it becomes the longer line.
93.98 %
42 votes

logic

Monk on a Path

A monk leaves at sunrise and walks on a path from the front door of his monastery to the top of a nearby mountain. He arrives at the mountain summit exactly at sundown. The next day, he rises again at sunrise and descends down to his monastery, following the same path that he took up the mountain. Assuming sunrise and sunset occured at the same time on each of the two days, prove that the monk must have been at some spot on the path at the same exact time on both days.
Imagine that instead of the same monk walking down the mountain on the second day, that it was actually a different monk. Let's call the monk who walked up the mountain monk A, and the monk who walked down the mountain monk B. Now pretend that instead of walking down the mountain on the second day, monk B actually walked down the mountain on the first day (the same day monk A walks up the mountain). Monk A and monk B will walk past each other at some point on their walks. This moment when they cross paths is the time of day at which the actual monk was at the same point on both days. Because in the new scenario monk A and monk B MUST cross paths, this moment must exist.
93.98 %
42 votes

logic

The stories of Emperor Akbar and Birbal

Emperor Akbar once ruled over India. He was a wise and intelligent ruler; and he had in his court the Nine Gems, his nine advisors, who were each known for a particular skill. One of these Gems was Birbal, known for his wit and wisdom. The story below is one of the examples of his wit. Do you have it in you to find the answer? One day the Emperor Akbar stumbled on a small rock in the royal gardens and momentarily went off balance. He was in a bad mood that day and the incident only served to make him more angry. Finding a target for his mood of the day, he ordered the gardener's arrest and execution. Birbal heard of this and visited the gardener in the cell where he was being held awaiting execution. Birbal had known the gardener for many years and also knew of the gardener's immense respect and sense of loyalty for the king. He decided to help the gardener escape the death sentence and explained his plan to the gardener, who reluctantly agreed to go along. The next day the gardener was asked what his last wish was before he was hanged, as was custom. The gardener requested an audience with the emperor. This wish was granted, but when the man neared the throne he tried to attack the emperor. The emperor was shocked and demanded an explanation. The gardener looked at Birbal, who stepped forward and explained why the gardener had attacked the emperor. The emperor immediately realised how unjust he had been and ordered the release of the gardener. How did Birbal manage this?
"Your Majesty," said Birbal, "there is probably no person more loyal to you than this unfortunate gardener. Fearing that people would say you hanged him for a silly reason and question your sense of justice, he went out of his way to give you a genuine reason for hanging him."
93.98 %
42 votes

logicprobability

Live or die probability puzzle

Hussey has been caught stealing goats, and is brought into court for justice. The judge is his ex-wife Amy Hussey, who wants to show him some sympathy, but the law clearly calls for two shots to be taken at Hussey from close range. To make things a little better for Hussey, Amy Hussey tells him she will place two bullets into a six-chambered revolver in successive order. She will spin the chamber, close it, and take one shot. If Hussey is still alive, she will then either take another shot, or spin the chamber again before shooting. Hussey is a bit incredulous that his own ex-wife would carry out the punishment, and a bit sad that she was always such a rule follower. He steels himself as Amy Hussey loads the chambers, spins the revolver, and pulls the trigger. Whew! It was blank. Then Amy Hussey asks, 'Do you want me to pull the trigger again, or should I spin the chamber a second time before pulling the trigger?' What should Hussey choose?
Hussey should have Amy Hussey pull the trigger again without spinning. We know that the first chamber Amy Hussey fired was one of the four empty chambers. Since the bullets were placed in consecutive order, one of the empty chambers is followed by a bullet, and the other three empty chambers are followed by another empty chamber. So if Hussey has Amy Hussey pull the trigger again, the probability that a bullet will be fired is 1/4. If Amy Hussey spins the chamber again, the probability that she shoots Hussey would be 2/6, or 1/3, since there are two possible bullets that would be in firing position out of the six possible chambers that would be in position.
93.98 %
42 votes

logicmathshort

Half of two plus two

Is half of two plus two equal to two or three?
Three. It seems that it could almost be either, but if you follow the mathematical orders of operation, division is performed before addition. So... half of two is one. Then add two, and the answer is three.
93.98 %
42 votes

cleanlogic

Three people in a hotel

Three people check into a hotel. They pay $30 to the manager and go to their room. The manager finds out that the room rate is $25 and gives $5 to the bellboy to return. On the way to the room, the bellboy reasons that $5 would be difficult to share among three people, so he pockets $2 and gives $1 to each person. Now, each person paid $10 and got back $1. So they paid $9 each, totalling $27. The bellboy has $2, totalling $29. ) Where is the remaining dollar?
Each person paid $9, totalling $27. The manager has $25 and the bellboy has $2. The bellboy's $2 should be added to the manager's $25 or substracted from the tenant's $27, not added to the tenants' $27.
93.98 %
42 votes

logic

Pink Island

It was a Pink Island. There were 201 individuals lived in the island. Among them 100 people were blue eyed people, 100 were green eyed people and the leader was a black eyed one. Except the leader, nobody knew how many individuals lived in the island. Neither have they known about the color of the eyes. The leader was a very strict person. Those people can never communicate with others. They even cannot make gestures to communicate. They can only talk and communicate with the leader. It was a prison for those 200 individuals. However, the leader provided an opportunity to leave the island forever but on one condition. Every morning he questions the individuals about the color of the eyes! If any of the individuals say the right color, he would be released. Since they were unaware about the color of the eyes, all 200 individuals remained silent. When they say wrong color, they were eaten alive to death. Afraid of punishment, they remained silent. One day, the leader announced that "at least 1 of you has green eyes! If you say you are the one, come and say, I will let you go if you are correct! But only one of you can come and tell me!" How many green eyed individuals leave the island and in how many days?
All 100 green eyed individuals will leave in 100 days. Consider, there is only one green eyed individual lived in the island. He will look at all the remaining individuals who have blue eyes. So, he can get assured that he has green eyes! If there were more than one green eyed people, when the first man looks at the second one with green eyes, the person didn’t leave on day the first day. It means he also has green eyes and the same rule applies to each green eyed man.
93.84 %
41 votes