You need to boil eggs for exactly 9 minutes. But you have only 2 hourglasses – one measures 4 minutes and the other measures 7 minutes. How do you measure exactly 9 minutes without the process taking longer than 9 minutes?.

You are given 1000 one dollar bills and 10 envelopes. Put the bills into the envelopes in such a way that someone can ask you for any amount of money from $1 to $1000 and you can give it to them through a combination of the envelopes.

A man has 53 socks in his drawer: 21 identical blue, 15 identical black and 17 identical red. The lights are fused and he is completely in the dark. How many socks must he take out to be 100 percent certain he has a pair of black socks?

In a pond there are some flowers with some bees hovering over the flowers. If each bee lands on a flower, one bee doesn’t get a flower. If two bees share each flower there is one flower left out. How many flowers and bees are there?

Find a 10 digit number where the first digit (most significant digit) indicates how many zeros are in the number, the second digit indicates how many 1s are in the number etc. till the tenth digit which indicates how many 9s are in the number.

There was a blind man. He had four socks in his drawer that were either black or white. He opened it and took out two socks. Now the probability that it was a pair of white socks is 1/2. Can you find out the probability of picking 2 black socks?

A swimming pool has four taps. The first can fill the entire pool with water in two days, the second in three days, the third in four days, and the last one can fill the pool in 6 hours. How long will it take to fill the pool using all 4 taps together?

Two trains start at the same time, one from London to Liverpool, the other from Liverpool to London. If they arrive at their destinations one hour and four hours respectively after passing one another, how much faster is one train running than the other?

Twelve flags stand equidistant along the track at the stadium. The runners start at the first flag. A runner reaches the eighth flag 8 seconds after he starts. If he runs at an even speed, how many seconds does he need altogether to reach the twelfth flag?

Gracie went for a morning walk and met her old friend Suzie and her daughter Jennie after a long time. Gracie asked Suzie how old is Jennie to which Jennie replied, “In two years i will be twice as old as I was five years ago”. How old is Jennie?

A zookeeper has to put 27 snakes in four cages. His problem is that he must have an odd number of snakes in each cage. How can he accomplish this? You can put any number of snakes in a cage as long as the total number of snakes in each cage is an odd number.

Daniel, my son, is exactly one fifth of my age. In 21 years time, I will be exactly twice his age. My wife is exactly seven times older than my daughter, Jessica. In 8 years time, my wife will be three times older then Jessica. How old are Daniel and Jessica now?

A fisherman’s day is rated as good if he catches 9 fishes, fair if 7 fishes and bad if 5 fishes. He catches 53 fishes in a week and had all good, fair and bad ratings in the week. So how many good, fair and bad ratings days did the fisherman had in the week?

Our man Ostap was going home from Kiev. He rode halfway by train – fifteen times as fast as he goes on foot. The second half he went by ox team. He can walk twice as fast as that. Would he have saved time if he had gone all the way on foot? If so, by how much?

A taxi driver was called to take a group of passengers to the train station. The station is normally an hour away, but with traffic being extra heavy, it took a full hour and a half. On the return trip the traffic was still as heavy but it took only 90 minutes. Why?