Best difficult riddles

interviewlogicmath

A bad king has a cellar of 1000 bottles of delightful and very expensive wine. A neighboring queen plots to kill the bad king and sends a servant to poison the wine. Fortunately (or say unfortunately) the bad king's guards catch the servant after he has only poisoned one bottle. Alas, the guards don't know which bottle but know that the poison is so strong that even if diluted 100,000 times it would still kill the king. Furthermore, it takes one month to have an effect. The bad king decides he will get some of the prisoners in his vast dungeons to drink the wine. Being a clever bad king he knows he needs to murder no more than 10 prisoners – believing he can fob off such a low death rate – and will still be able to drink the rest of the wine (999 bottles) at his anniversary party in 5 weeks time. Explain what is in mind of the king, how will he be able to do so?
Think in terms of binary numbers. (now don’t read the solution, give a try). Number the bottles 1 to 1000 and write the number in binary format. bottle 1 = 0000000001 (10 digit binary) bottle 2 = 0000000010 bottle 500 = 0111110100 bottle 1000 = 1111101000 Now take 10 prisoners and number them 1 to 10, now let prisoner 1 take a sip from every bottle that has a 1 in its least significant bit. Let prisoner 10 take a sip from every bottle with a 1 in its most significant bit. etc. prisoner = 10 9 8 7 6 5 4 3 2 1 bottle 924 = 1 1 1 0 0 1 1 1 0 0 For instance, bottle no. 924 would be sipped by 10,9,8,5,4 and 3. That way if bottle no. 924 was the poisoned one, only those prisoners would die. After four weeks, line the prisoners up in their bit order and read each living prisoner as a 0 bit and each dead prisoner as a 1 bit. The number that you get is the bottle of wine that was poisoned. 1000 is less than 1024 (2^10). If there were 1024 or more bottles of wine it would take more than 10 prisoners.
80.29 %
55 votes
logicsimpleclean

Two convicts are locked in a cell. There is an unbarred window high up in the cell. No matter if they stand on the bed or one on top of the other they can't reach the window to escape. They then decide to tunnel out. However, they give up with the tunnelling because it will take too long. Finally one of the convicts figures out how to escape from the cell. What is his plan?
His plan is to dig the tunnel and pile up the dirt to climb up to the window to escape.
80.15 %
61 votes
logicsimpleclean

There is a small town in the midwest with exactly 2 barbershops, one on each side of town. The barbershop on the west side of town is pristine. Its floors are spotless, the windows are always perfectly clear, and the air always smells fresh. The barber has a friendly smile, shined shoes, a well-groomed head of hair, and a fancy shirt. The barbershop on the east side of town is a mess. Its floors and windows are dirty, and the air smells of garbage. The barber always has a grimace on his face. His skin is oily, his hair is short and ragged, and he has food on his clothes all the time. A man travelling through the town realizes he needs a haircut. Knowing the stories of the two barbers, the man decides to go to the dirty barbershop on the east side of town. Why does he do this?
Because there are only two barbers in the town, the barbers must cut each-other's hair. The barber on the west side of town has a nice haircut, so the east-side barber must be a good barber. On the other hand, the barber on the east side of town has ragged hair, meaning the west-side barber must not be very good. So the man goes to the east-side barber to get a better haircut.
80.14 %
48 votes