There was an aeroplane crash, every single person died, but two people survived. How is this possible?

Solve the below puzzle by replacing the question mark with the correct number.

3 6 12

4 8 16

5 10 ?

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

My thunder comes before the lightning; my lightning comes before clouds; my rain dries all the land it touches. What am I?

You stand in front of two doors. A guard stands next to each door. You know the following things: one path leads to paradise, the other leads to death. You cannot distinguish between the two doors. You also know that one of the two guards always tells the truth and the other always lies. You have permission to ask one guard one question to discover which door leads to paradise. What one question would you ask to guarantee you enter the door to paradise?

Can you find the odd number in the following?

2716, 4135, 5321 and 7145

John was so frustrated to be the suspect of being a sleeper terrorist that he shoot himself right between the eyes with a revolver in his toilet. The revolver and the bullets were accurate. Minutes later John walks out of the toilet unharmed.
How can this be possible?

In a university, a professor gave a set of three problems to the three brilliant students of his class. See the image for the questions.

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

Railroad Crossing, look out for the cars. Can you spell that, without any R's ?