You have two strings whose only known property is that when you light one end of either string it takes exactly one hour to burn. The rate at which the strings will burn is completely random and each string is different.

How do you measure 45 minutes?

How many words can a pen with half refill write?

An infinite number of mathematicians are standing behind a bar. The first asks the barman for half a pint of beer, the second for a quarter pint, the third an eighth, and so on. How many pints of beer will the barman need to fulfill all mathematicians' wishes?

A doctor and a boy were fishing. The boy was the doctor’s son, but the doctor was not the boy’s father. Who was the doctor?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

No one wants to have it, but if one got it, he does not want to lose it. What is It?

If 24H in a D => 24 hours in a day.
What does "64S on CB" stand for?

During which month do people sleep the least?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?