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?

Can you find out the missing number in the grid?

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?

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 ?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?

Can you find the mistake in the below statement?

"That Restaurant always remains crowded. This is the reason why nobody goes there".

Can you find a flaw in this statement?

What happened when the wheel was invented?

In the figure, you can see nine stars. What you have to do is connect all of them by using just four line and without lifting your hand i.e. in a continuous flow.