logicWhen Manish was three years old he carved a nail into his favorite tree to mark his height. Six years later at age nine, Manish returned to see how much higher the nail was. If the tree grew by five centimeters each year, how much higher would the nail be.

The nail would be at the same height since trees grow at their tops.

## Similar riddles

See also best riddles or new riddles.

logicmathIf you have two coins which total 35 cents and one of the coins is not a dime, what are the two coins?

A quarter and a dime. One coin is not a dime, but the other one is.

logicshortWhat always comes into a house through the keyhole?

A key.

animallogicshortI eat other animals.
I have a big mouth.
I am green.
I live in the water.
Who am I?

I am a crocodile.

logicmysteryAn American, who had never been to any country other than the United States, travelled a long way to see a sight that very few people had seen. He was standing one day on solid ground when he saw the Great Wall of China with his own eyes. How come?

He was an astronaut standing on the moon - from where the Great Wall of China is visible.

logicThe Pope, Beyonce, Barack Obama, and Bill Gates are on the same plane.
There are only 3 parachutes left for the 4 of them.
Obama says: "As the President, I think I should have the right to have a parachute, because I rule millions of people in the greatest nation of all."
Beyonce says: "As one of the greatest singers of all-time, I think I should deserve to be safe. I bring tears and laughter to millions of people, and I'm an important contributor to pop music."
Bill Gates says: "As one of the richest successful company owners, I think I should live because I'm on top of the economics cycle, creating jobs and incomes for millions of people. I am a wealthy and intelligent man."
Finally, the Pope says: "I'm an old, religious man. I lived a life that's full, I helped millions of people find their way through God, I'm ready to let go of a parachute and to face my fate."
Which one of them will abandon the parachute and die?

Did I ever mention that the plane was crashing? No one's gonna die.

interviewlogicmathThree 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?

So let’s think this through. The ants can only avoid a collision if they all decide to move in the same direction (either clockwise or anti-clockwise). If the ants do not pick the same direction, there will definitely be a collision. Each ant has the option to either move clockwise or anti-clockwise. There is a one in two chance that an ant decides to pick a particular direction. Using simple probability calculations, we can determine the probability of no collision.
P(No collision) = P(All ants go in a clockwise direction) + P( All ants go in an anti-clockwise direction) = 0.5 * 0.5 * 0.5 + 0.5 * 0.5 * 0.5 = 0.25

crazyfunnylogicshortWhat's round and bad-tempered?

A vicious circle.

funnylogicJoe bets Tony $100 that he can predict the score of the football game before it starts. Tony agrees, but loses the bet. Why did Tony lose the bet?

Joe said the score would be 0-0 and he was right. "Before" any football game starts, the score is always 0-0.

cleanEinstein’slogicFive friends have their gardens next to one another, where they grow three kinds of crops: fruits (apple, pear, nut, cherry), vegetables (carrot, parsley, gourd, onion) and flowers (aster, rose, tulip, lily).
They grow 12 different varieties.
Everybody grows exactly 4 different varieties
Each variety is at least in one garden.
Only one variety is in 4 gardens.
Only in one garden are all 3 kinds of crops.
Only in one garden are all 4 varieties of one kind of crops.
Pears are only in the two border gardens.
Paul's garden is in the middle with no lily.
Aster grower doesn't grow vegetables.
Rose grower doesn't grow parsley.
Nuts grower has also gourd and parsley.
In the first garden are apples and cherries.
Only in two gardens are cherries.
Sam has onions and cherries.
Luke grows exactly two kinds of fruit.
Tulips are only in two gardens.
Apples are in a single garden.
Only in one garden next to the Zick's is parsley.
Sam's garden is not on the border.
Hank grows neither vegetables nor asters.
Paul has exactly three kinds of vegetable.
Who has which garden and what is grown where?

logicmathThere are 1 million closed school lockers in a row, labeled 1 through 1,000,000.
You first go through and flip every locker open.
Then you go through and flip every other locker (locker 2, 4, 6, etc...). When you're done, all the even-numbered lockers are closed.
You then go through and flip every third locker (3, 6, 9, etc...). "Flipping" mean you open it if it's closed, and close it if it's open. For example, as you go through this time, you close locker 3 (because it was still open after the previous run through), but you open locker 6, since you had closed it in the previous run through.
Then you go through and flip every fourth locker (4, 8, 12, etc...), then every fifth locker (5, 10, 15, etc...), then every sixth locker (6, 12, 18, etc...) and so on. At the end, you're going through and flipping every 999,998th locker (which is just locker 999,998), then every 999,999th locker (which is just locker 999,999), and finally, every 1,000,000th locker (which is just locker 1,000,000).
At the end of this, is locker 1,000,000 open or closed?

Locker 1,000,000 will be open.
If you think about it, the number of times that each locker is flipped is equal to the number of factors it has. For example, locker 12 has factors 1, 2, 3, 4, 6, and 12, and will thus be flipped 6 times (it will end be flipped when you flip every one, every 2nd, every 3rd, every 4th, every 6th, and every 12th locker). It will end up closed, since flipping an even number of times will return it to its starting position. You can see that if a locker number has an even number of factors, it will end up closed. If it has an odd number of factors, it will end up open.
As it turns out, the only types of numbers that have an odd number of factors are squares. This is because factors come in pairs, and for squares, one of those pairs is the square root, which is duplicated and thus doesn't count twice as a factor. For example, 12's factors are 1 x 12, 2 x 6, and 3 x 4 (6 total factors). On the other hand, 16's factors are 1 x 16, 2 x 8, and 4 x 4 (5 total factors).
So lockers 1, 4, 9, 16, 25, etc... will all be open. Since 1,000,000 is a square number (1000 x 1000), it will be open as well.