Replace the question mark with the correct number in the below-given picture?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

I have a five and a three-gallon jar. Assuming there is an infinite supply of water, how can I measure one-gallon water?

The centre of the third figure is empty. What digit should fit inside?

You find yourself in a strange place guarded by two guards.One of the guard always say truth while other always lies.You don't know the identity of the two.You can ask only one question to go out from there. What should you ask?

There are 2 sand hourglasses.

The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?

In the figure that has been attached to this question, each digit represents a digit. The similar letters carry the same integer value. Can you expose the original digits?

A man is found dead with a knife in his back When the investigation is done. A chair lays beside him and the forensic team finds moisture around the body.

If he committed suicide, how did he do it?

If,

6 / 7 = 2
3 / 9 = 7
8 / 2 = 6

Then

4 / 5 = ?

Which word is least like the others? Third, fourth, fifth, sixth, seventh, eighth, ninth?