What four weights can be used to balance from 1 to 30 pounds?

You are an expert on paranormal activity and have been hired to locate a spirit haunting an old resort hotel. Strong signs indicate that the spirit lies behind one of four doors. The inscriptions on each door read as follows:

Door A: It's behind B or C
Door B: Its behind A or D
Door C: It's in here
Door D: It's not in here

Your psychic powers have told you three of the inscriptions are false, and one is true. Behind which door will you find the spirit?

Count the number of triangles in the below picture?

As you can see that fifteen matches have been used to form an arrangement. What you have to do is remove any six of them to make them ten.

What is the fastest way to double your money?

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

Prove that twice of ten is the same as twice of eleven.

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?

It has horns but can’t beep. It is like to bleat but It is not a sheep. What is it?

Can you identify if it's a murder or a suicide ?