Can you solve this amazing hard number series problem?
7, 8, 10, 12, 16, 18 ?

Replace the question mark in the picture below.

I make two people out of one. What am I?

A convention is held where all the big logicians are summoned. The master places a band on everyone's forehead. Now all of them can see others bands but can't see his own. Then they are told that there are different colours of bands. All the logicians sit in circle and they are further explained that a bell will ring at regular intervals. The moment when a logician knew the colour of band on his forehead, he will leave at the next bell. If anyone leaves at the wrong bell, he will be disqualified.

The master assures the logicians that the puzzle will not be impossible for anyone of them. How will the logicians manage ?

In the Chess Board picture below white army is arranged. You need to add a black army on the board such that no piece is under any threat.
Note: Army comprised of 1 king, 1 queen, 2 rooks, 2 bishops, 2 knights, and 8 pawns.

How many times can you subtract the number two from the number fifty?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

Find The Missing Number In the Sequence.
6 25 64 ? 32 1

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?

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?