Can you place six X (crosses) in below board without making three in a row in any way ?

Solve the following series:
AZ, GT, MN, __, YB

A high school has a strange principal. On the first day, he has his students perform an odd opening day ceremony:

There are one thousand lockers and one thousand students in the school. The principal asks the first student to go to every locker and open it. Then he has the second student go to every second locker and close it. The third goes to every third locker and, if it is closed, he opens it, and if it is open, he closes it. The fourth student does this to every fourth locker, and so on. After the process is completed with the thousandth student, how many lockers are open?

When is the top of a mountain similar to a savings account?

Double it and multiply it by 4. Then divide it by 8 and you’ll have it once more. What number is it?

Rectify the following equality 101 - 102 = 1 by moving just one digit.

I travel all around the world but always stay in the corner. What am I?

Can you count the number of lines in the below picture?

How old is your son? asked a man to his neighbour. My son is five times as old as my daughter and my wife is five times as old as my son. I am twice as old as my wife whereas my grandmother, who is celebrating her eighty-first birthday is as old as all of us put together.

How old is the man's son ?

If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door?