Hard riddles

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.
77.37 %
53 votes

logicmathshort

Leave 6

Take 9 from 6, 10 from 9, 50 from 40 and leave 6. How is it possible?
SIX - 9 (IX) = S 9 (IX) - 10 (X) = I 40 (XL) - 50 (L) = X
76.74 %
46 votes

cleanfunnylogiclove

Love triangle

A doctor and a bus driver are both in love with the same woman, an attractive girl named Sarah. The bus driver had to go on a long bustrip that would last a week. Before he left, he gave Sarah seven apples. Why?
An apple a day keeps the doctor away!
76.73 %
182 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.
76.26 %
66 votes

logic

The farmer, the engineer, the physicist, and the mathematician

A farmer challenges an engineer, a physicist, and a mathematician to fence off the largest amount of area using the least amount of fence. The engineer made his fence in a circle and said it was the most efficient. The physicist made a long line and said that the length was infinite. Then he said that fencing half of the Earth was the best. The mathematician laughed at the others and with his design, beat the others. What did he do?
75.57 %
59 votes

cleanlogicwhat am I

Move very slowly

I move very slowly at an imperceptible rate, although I take my time, I am never late. I accompany life, and survive past demise, I am viewed with esteem in many women's eyes. What am I?
I am your hair.
75.57 %
64 votes

cleanfunnylogicshort

A millionaire

A kind hearted person Mr. Rawat buy packed food at 3$/packet from United states and sells them at 1$/packet at Africa. After some time he becomes a millionaire. How come the guy become millionaire?
He started out as a billionaire, but lost so much money in his good works (by giving to poor people) that he became a millionaire.
73.31 %
85 votes

logicprobability

Russian roulette choice

Your enemy challenges you to play Russian Roulette with a 6-cylinder pistol (meaning it has room for 6 bullets). He puts 2 bullets into the gun in consecutive slots, and leaves the next four slots blank. He spins the barrel and hands you the gun. You point the gun at yourself and pull the trigger. It doesn't go off. Your enemy tells you that you need to pull the trigger one more time, and that you can choose to either spin the barrel at random, or not, before pulling the trigger again. Spinning the barrel will position the barrel in a random position. Assuming you'd like to live, should you spin the barrel or not before pulling the trigger again?
You are better off shooting again without spinning the barrel. Given that the gun didn't fire the first time, it was pointing to one of the four empty slots. Because your enemy spun the cylinder randomly, it would have been pointing to any of these empty slots with equal probability. Three of these slots would not fire again after an additional trigger-pull, and one of them would. Thus, by not spinning the barrel, there is a 1/4 chance that pulling the trigger again would fire the gun. Alternatively, if you spin the barrel, it will point to each of the 6 slots with equal probability. Because 2 of these 6 slots have bullets in them, there would be a 2/6 = 1/3 chance that the gun would fire after spinning the barrel. Thus, you are better off not spinning the barrel.
73.22 %
58 votes