Best riddles

logicmath

Six bills

How could you give someone $63 using six bills without using one dollar bills?
1 - $50 bill, 1 - $5 bill, 4 - $2 bills.
92.02 %
31 votes

cleanshort

No man can own me, yet I encompass what all men must have

I look flat, but I am deep, Hidden realms I shelter. Lives I take, but food I offer. At times I am beautiful. I can be calm, angry and turbulent. I have no heart, but offer pleasure as well as death. No man can own me, yet I encompass what all men must have.
Ocean.
92.00 %
53 votes

logicshort

Clever thief sentenced to death

In olden days you are a clever thief charged with treason against the king and sentenced to death. But the king decides to be a little lenient and lets you choose your own way to die. What way should you choose? Remember, your're clever!
I would have chosen to die of "old age". Did you?
91.86 %
52 votes

logic

German/Swiss border

A woman who lived in Germany during World War II wanted to cross the German/Swiss border in order to escape Nazi pursuers. The bridge which she is to cross is a half mile across, over a large canyon. Every three minutes a guard comes out of his bunker and checks if anyone is on the bridge. If a person is caught trying to escape German side to the Swiss side they are shot. If caught crossing the other direction without papers they are sent back. She knows that it takes at least five minutes to cross the bridge, in which time the guard will see her crossing and shoot her. How does she get across?
She waits until the guard goes inside his hunt, and begins to walk across the bridge. She gets a little more than half way, turns around, and begins to walk toward the geman side once more. The guard comes out, sees that she has no papers, and sends her "back" to the swiss side.
91.86 %
52 votes

logicmathprobability

The same birthday

What is the least number of people that need to be in a room such that there is greater than a 50% chance that at least two of the people have the same birthday?
Only 23 people need to be in the room. Our first observation in solving this problem is the following: (the probability that at least 2 people have the same birthday + the probability that nobody has the same birthday) = 1.0 What this means is that there is a 100% chance that EITHER everybody in the room has a different birthday, OR at least two people in the room have the same birthday (and these probabilities don't add up to more than 1.0 because they cover mutually exclusive situations). With some simple re-arranging of the formula, we get: the probability that at least 2 people have the same birthday = (1.0 - the probability that nobody has the same birthday) So now if we can find the probability that nobody in the room has the same birthday, we just subtract this value from 1.0 and we'll have our answer. The probability that nobody in the room has the same birthday is fairly straightforward to calculate. We can think of this as a "selection without replacement" problem, where each person "selects" a birthday at random, and we then have to figure out the probability that no two people select the same birthday. The first selection has a 365/365 chance of being different than the other birthdays (since none have been selected yet). The next selection has a 364/365 chance of being different than the 1 birthday that has been selected so far. The next selection has a 363/365 chance of being different than the 2 birthdays that have been selected so far. These probabilities are multiplied together since each is conditional on the previous. So for example, the probability that nobody in a room of 3 people have the same birthday is (365/365 * 364/365 * 363/365) =~ 0.9918 More generally, if there are n people in a room, then the probability that nobody has the same birthday is (365/365 * 364/365 * ... * (365-n+2)/365 * (365-n+1)/365) We can plug in values for n. For n=22, we get that the probability that nobody has the same birthday is 0.524, and thus the probabilty that at least two people have the same birthday is (1.0 - 0.524) = 0.476 = 47.6%. Then for n=23, we get that the probability that nobody has the same birthday is 0.493, and thus the probabilty that at least two people have the same birthday is 1.0 - 0.493) = 0.507 = 50.7%. Thus, once we get to 23 people we have reached the 50% threshold.
91.86 %
52 votes

cleanfunnyshort

Two cups

You have two cups. One cup is filled with black coffee and another cup is filled with black tea. Both cups are filled with equal quantity of respective beverages. Take one spoonful of black tea and mix with the cup of black coffee. Then take one spoonful of black coffee and mix it with the cup of black tea. Now tell, me which cup has more liquid in it? Does the cup of black tea has more liquid or black coffee has more liquid?
Both cups have equal quantity of respective drink. You take one spoonful from tea and mix it with coffee and vice versa.
91.77 %
30 votes

You want me, when you don't have me

When you don't have me, you want me, but when you do have me, you want to give me away. What am I?
A secret.
91.77 %
30 votes

Travel around the world

What can travel around the world while staying in a corner?
A stamp.
91.77 %
30 votes