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?

I look at you, you look at me I raise my right, you raise your left. What am I?

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?

You can see three almost identical images below. Can you spot the odd one out from them?

A plane crashed between the border of Mexico and America. Where do you bury the survivors?

How many triangles are there on the puzzle below?

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

What numbers should go on the bottom line?
3 6 9 15
8 2 10 12
11 8 19 27
19 10 29 39
? ? ? ?

When can we add 2 to 11 and get 1 as the correct answer?

Who can jump higher than a Mountain?