If it took eight men ten hours to build a wall, how long would it take four men to build it?

Can you count the number of quadrilaterals in the picture below?

Replace the question mark with the number below given a simple math problem.

The teacher told the student that if he told a lie then he will be expelled from school and if he told the truth then he still is expelled from school.

What can a student say to prevent his being expelled from school?

How is a fly different from a mosquito?

You are in a room with no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify which one is a magnet?

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

Move three sticks of the spiral below to form a square.

After a heavy Thanksgiving meal, the night watchman went to work. In the morning, he told his boss he had dreamed that a saboteur planted a bomb in the factory and that he felt it was a warning. The boss promptly fired him. Worker confused, Why boss fire him?

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?