How can a man go eight days without sleep?

Can you replace the question mark with the correct number in the below table sequence?

O_er_t_o_

Complete the missing letters of the given word.

Can you solve the tricky chess rebus puzzle below by ciphering the hidden meaning?

Given that

(78)^9 = 6
And (69)^4 = 11

Can you find out

(99)^2 =?

(Note: This is Logical, not Mathematical)

Can you circle exactly four of these numbers such that the total is twelve?

1 6 1
6 1 6
1 6 1
6 1 6

A pack of cards has 40 cards. You are blindfolded. Out of 40, 25 cards are facing down while 15 are facing up. You have been asked to divide this pack of cards into two decks - so that each deck contains an equal number of face-up cards. Remember, you are blindfolded.

How will you do it?

I had an infinite supply of water and 5 litres and 3 litres jars.

How would you measure exactly 4 litres in the least number of steps?

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?

In the image below, can you find the value of an angle(y)