Can you think of a smallest +ve number such that if we shuffle the digits of the number, the new number becomes double the original number?

You have two hour glasses one measures 7 minutes and the other measures 4 minutes.
Using these two-hour glasses, you need to measure exactly 9 minutes.

How come?

If a shopkeeper can only place the weights on one side of the common balance. For example, if he has weights 1 and 3 then he can measure 1, 3 and 4 only. Now the question is how many minimum weights and names of the weights you will need to measure all weights from 1 to 1000? This is a fairly simple problem and very easy to prove also.

How can a man go eight days without sleep?

Count the number of lines in the image below ?

I start and end with 500 and carry a 5 in my heart. But I require the first letter and the first number to be complete. I am the name of a King.

Who am I ?

Can you write down eight eights so that they add up to one thousand?

In a science lab, a petri dish hosts a healthy colony of yeast for an experiment. Now every minute, all the yeast cells divide into two. At noon, there was just a single cell of yeast and at 1:22, the Petri dish was half full. Can you calculate when the dish will be full of yeast?

There once were seven dwarfs who were all brothers. They were all born two years apart. The youngest dwarf is seven years old. How old is his oldest brother?

Count the number of squares in the picture below.